laplace transform mcq questions with solution

laplace transform mcq 100 questions with solution

Laplace Transform MCQs Q1-Q25

🔵 Laplace Transform

100 MCQs with Detailed Step-by-Step Solutions

📘 Mathematics 📝 MCQ Practice 🧠 Detailed Solution 🎯 Q1–Q25
🟣 Part 1 — Basic Laplace Transform
Question 1
Find the Laplace transform of 1.
A) s
B) 1/s
C) s²
D) 0
🟢 Correct Answer: B) 1/s
🟡 Formula
L{f(t)} = ∫0 e-stf(t)dt
🔵 Step-by-Step Solution

Here,

f(t) = 1

Therefore:

L{1} = ∫0 e-stdt

Integrating:

∫e-stdt = −e-st s

Applying the limits:

[ −e-st s ]0

For s > 0:

e-s∞ = 0

Hence:

0 − ( −1 s ) = 1 s
🔴 Final Result: L{1} = 1 s
Question 2
Find the Laplace transform of t.
A) 1/s
B) 1/s²
C) 2/s
D) s²
🟢 Correct Answer: B) 1/s²
🟡 Formula
L{tn} = n! sn+1
🔵 Step-by-Step Solution

Here:

n = 1

Therefore:

L{t} = 1!

Since 1! = 1:

L{t} = 1
🔴 Final Result: 1
Question 3
Find the Laplace transform of t².
A) 1/s²
B) 2/s³
C) 2/s²
D) 1/s³
🟢 Correct Answer: B) 2/s³
🟡 Formula
L{tn} = n! sn+1
🔵 Step-by-Step Solution

Put n = 2:

L{t²} = 2!

Since:

2! = 2 × 1 = 2

Therefore:

L{t²} = 2
🔴 Final Result: 2/s³
Question 4
Find the Laplace transform of t³.
A) 3/s⁴
B) 6/s⁴
C) 9/s⁴
D) 1/s³
🟢 Correct Answer: B) 6/s⁴
🔵 Step-by-Step Solution
L{t³} = 3! s⁴

Now:

3! = 3 × 2 × 1 = 6

Therefore:

L{t³} = 6 s⁴
🔴 Final Result: 6/s⁴
Question 5
Find the Laplace transform of eat.
A) 1/(s+a)
B) 1/(s-a)
C) a/(s-a)
D) s/(s-a)
🟢 Correct Answer: B) 1/(s-a)
🟡 Formula
L{eat} = 1 s − a
🔵 Step-by-Step Solution

Using the definition:

L{eat} = ∫0 e-steatdt

Combine the exponential terms:

e-steat = e-(s-a)t

Therefore:

0 e-(s-a)tdt = 1 s − a
🔴 Final Result: 1/(s-a)
Question 6
Find the Laplace transform of e-at.
A) 1/(s-a)
B) 1/(s+a)
C) a/(s+a)
D) s/(s-a)
🟢 Correct Answer: B) 1/(s+a)
🔵 Step-by-Step Solution

Start with:

L{eat} = 1 s − a

Replace a by −a:

L{e-at} = 1 s − (−a)

Therefore:

L{e-at} = 1 s + a
🔴 Final Result: 1/(s+a)
Question 7
Find the Laplace transform of sin(at).
A) s/(s²+a²)
B) a/(s²+a²)
C) a/(s²-a²)
D) 1/s
🟢 Correct Answer: B) a/(s²+a²)
🟡 Standard Formula
L{sin(at)} = a s² + a²
🔵 Explanation

The standard Laplace transform of sin(at) is:

L{sin(at)} = a s² + a²

For example, if a = 3:

L{sin(3t)} = 3 s² + 9
🔴 Final Result: a/(s²+a²)
Question 8
Find the Laplace transform of cos(at).
A) a/(s²+a²)
B) s/(s²+a²)
C) s/(s²-a²)
D) 1/(s+a)
🟢 Correct Answer: B) s/(s²+a²)
🟡 Standard Formula
L{cos(at)} = s s² + a²
🔵 Explanation

Using the standard Laplace transform:

L{cos(at)} = s s² + a²

For example:

L{cos(2t)} = s s² + 4
🔴 Final Result: s/(s²+a²)
Question 9
Find the Laplace transform of sinh(at).
A) a/(s²+a²)
B) s/(s²-a²)
C) a/(s²-a²)
D) 1/(s-a)
🟢 Correct Answer: C) a/(s²-a²)
🟡 Formula
L{sinh(at)} = a s² − a²
🔵 Step-by-Step Solution

Use the identity:

sinh(at) = eat − e-at 2

Taking Laplace transform:

L{sinh(at)} = 1 2 [ 1 s−a 1 s+a ]

Taking common denominator:

= a s²−a²
🔴 Final Result: a/(s²-a²)
Question 10
Find the Laplace transform of cosh(at).
A) a/(s²-a²)
B) s/(s²-a²)
C) s/(s²+a²)
D) 1/s
🟢 Correct Answer: B) s/(s²-a²)
🟡 Formula
L{cosh(at)} = s s² − a²
🔵 Step-by-Step Solution

Use:

cosh(at) = eat + e-at 2

Taking Laplace transform:

L{cosh(at)} = 1 2 [ 1 s−a + 1 s+a ]

After simplifying:

L{cosh(at)} = s s²−a²
🔴 Final Result: s/(s²-a²)
🟠 Part 2 — Linearity
Question 11
If L{f(t)} = F(s) and L{g(t)} = G(s), find L{af(t)+bg(t)}.
A) aF(s)+bG(s)
B) F(s)G(s)
C) a+b+F(s)
D) F(s)/G(s)
🟢 Correct Answer: A) aF(s)+bG(s)
🟡 Linearity Property
L{af(t)+bg(t)} = aL{f(t)}+bL{g(t)}
🔵 Step-by-Step Solution

Given:

L{f(t)}=F(s)
L{g(t)}=G(s)

Therefore:

L{af(t)+bg(t)} = aF(s)+bG(s)
🔴 Final Result: aF(s)+bG(s)
Question 12
If L{f(t)} = F(s), find L{3f(t)}.
A) F(s)/3
B) 3F(s)
C) F(s)+3
D) F(3s)
🟢 Correct Answer: B) 3F(s)
🔵 Step-by-Step Solution

Using the constant multiplication property:

L{3f(t)} = 3L{f(t)}

Since L{f(t)} = F(s):

L{3f(t)}=3F(s)
🔴 Final Result: 3F(s)
Question 13
Find the Laplace transform of 2 + 3t.
A) 2/s + 3/s²
B) 2/s² + 3/s
C) 5/s²
D) 2s + 3s²
🟢 Correct Answer: A)
🔵 Step-by-Step Solution

Using linearity:

L{2+3t} = L{2}+L{3t}

Now:

L{2} = 2 s
L{3t} = 3 1

Therefore:

L{2+3t} = 2 s + 3
🔴 Final Result: 2/s + 3/s²
Question 14
Find the Laplace transform of 4t² + 5.
A) 8/s³ + 5/s
B) 4/s² + 5/s
C) 8/s² + 5/s³
D) 4/s³ + 5/s
🟢 Correct Answer: A)
🔵 Step-by-Step Solution
L{4t²+5} = 4L{t²}+5L{1}

We know:

L{t²} = 2

Therefore:

4 2 = 8

Also:

L{5} = 5 s

Hence:

L{4t²+5} = 8 + 5 s
🔴 Final Result: 8/s³ + 5/s
Question 15
Find the Laplace transform of 5e2t.
A) 5/(s+2)
B) 5/(s-2)
C) 2/(s-5)
D) 1/(s-10)
🟢 Correct Answer: B)
🟡 Formula
L{eat} = 1 s−a
🔵 Step-by-Step Solution

Here a = 2.

L{e2t} = 1 s−2

Multiplying by 5:

L{5e2t} = 5 s−2
🔴 Final Result: 5/(s−2)
Question 16
Find the Laplace transform of 3sin(2t).
A) 2/(s²+4)
B) 3/(s²+4)
C) 6/(s²+4)
D) 3s/(s²+4)
🟢 Correct Answer: C)
🔵 Step-by-Step Solution

Use:

L{sin(at)} = a s²+a²

Here a = 2:

L{sin(2t)} = 2 s²+4

Multiply by 3:

3 × 2 s²+4 = 6 s²+4
🔴 Final Result: 6/(s²+4)
Question 17
Find the Laplace transform of 4cos(3t).
A) 12/(s²+9)
B) 4s/(s²+9)
C) 3s/(s²+4)
D) 4/(s²+9)
🟢 Correct Answer: B)
🔵 Step-by-Step Solution
L{cos(at)} = s s²+a²

For a = 3:

L{cos(3t)} = s s²+9

Multiply by 4:

= 4s s²+9
🔴 Final Result: 4s/(s²+9)
Question 18
Find the Laplace transform of t⁴.
A) 4/s⁵
B) 24/s⁵
C) 12/s⁴
D) 24/s⁴
🟢 Correct Answer: B)
🔵 Step-by-Step Solution
L{t⁴} = 4! s⁵

Since:

4! = 4×3×2×1 = 24

Therefore:

L{t⁴} = 24 s⁵
🔴 Final Result: 24/s⁵
Question 19
Find the Laplace transform of 6t³.
A) 6/s⁴
B) 18/s⁴
C) 36/s⁴
D) 12/s⁴
🟢 Correct Answer: C)
🔵 Step-by-Step Solution

We know:

L{t³} = 6 s⁴

Therefore:

L{6t³} = 6 6 s⁴
= 36 s⁴
🔴 Final Result: 36/s⁴
Question 20
Find the Laplace transform of 7.
A) 7s
B) 7/s
C) 1/(7s)
D) s/7
🟢 Correct Answer: B)
🔵 Step-by-Step Solution

We know:

L{1} = 1 s

Therefore:

L{7} = 7L{1}
= 7 s
🔴 Final Result: 7/s
🔴 Part 3 — Laplace Transform of Derivatives
Question 21
If F(s) = L{f(t)}, find L{f'(t)}.
A) sF(s)
B) sF(s)-f(0)
C) F(s)/s
D) F'(s)
🟢 Correct Answer: B) sF(s)-f(0)
🟡 Formula
L{f'(t)} = sF(s)−f(0)
🔵 Step-by-Step Solution

By the derivative property of the Laplace transform:

L{f'(t)} = sL{f(t)}−f(0)

Since:

L{f(t)}=F(s)

we get:

L{f'(t)} = sF(s)−f(0)

The initial value f(0) is therefore included automatically in the transformed derivative.

🔴 Final Result: sF(s) − f(0)
Question 22
Find the Laplace transform of f”(t).
A) s²F(s)
B) s²F(s)-sf(0)-f'(0)
C) sF(s)-f(0)
D) F(s)/s²
🟢 Correct Answer: B)
🟡 Formula
L{f”(t)} = s²F(s)−sf(0)−f'(0)
🔵 Step-by-Step Solution

We know:

L{f'(t)} = sF(s)−f(0)

Apply the same derivative rule again:

L{f”(t)} = sL{f'(t)}−f'(0)

Substitute:

= s[sF(s)−f(0)]−f'(0)

Expand:

= s²F(s)−sf(0)−f'(0)
🔴 Final Result: s²F(s) − sf(0) − f'(0)
Question 23
Find the Laplace transform of f”'(t).
A) s³F(s)
B) s³F(s)-s²f(0)-sf'(0)-f”(0)
C) sF(s)-f(0)
D) F(s)/s³
🟢 Correct Answer: B)
🟡 Formula
L{f”'(t)} = s³F(s)−s²f(0)−sf'(0)−f”(0)
🔵 Step-by-Step Solution

From the second derivative:

L{f”} = s²F−sf(0)−f'(0)

Now take the transform of the third derivative:

L{f”’} = sL{f”}−f”(0)

Substitute the previous result:

= s[s²F−sf(0)−f'(0)]−f”(0)

Expand:

= s³F−s²f(0)−sf'(0)−f”(0)
🔴 Final Result: s³F(s) − s²f(0) − sf'(0) − f”(0)
Question 24
If f(0) = 2, find L{f'(t)}.
A) sF(s)+2
B) sF(s)-2
C) F(s)-2
D) 2F(s)
🟢 Correct Answer: B) sF(s)-2
🟡 Formula
L{f'(t)} = sF(s)−f(0)
🔵 Step-by-Step Solution

Given:

f(0)=2

Using the formula:

L{f'(t)} = sF(s)−f(0)

Substitute f(0) = 2:

L{f'(t)} = sF(s)−2
🔴 Final Result: sF(s) − 2
Question 25
If f(0) = 0, find L{f'(t)}.
A) sF(s)
B) F(s)/s
C) F'(s)
D) 0
🟢 Correct Answer: A) sF(s)
🟡 Formula
L{f'(t)} = sF(s)−f(0)
🔵 Step-by-Step Solution

Given:

f(0)=0

Substitute into the derivative formula:

L{f'(t)} = sF(s)−0

Therefore:

L{f'(t)}=sF(s)
🔴 Final Result: sF(s)
Laplace Transform MCQs Q26-Q50

🔵 Laplace Transform

100 MCQs with Detailed Step-by-Step Solutions

📘 Mathematics 📝 MCQ Practice 🧠 Detailed Solution 🎯 Q26–Q50
🟢 Part 2 — Important Properties of Laplace Transform
Question 26
If L{f(t)} = F(s), find L{tf(t)}.
A) −F′(s)
B) F′(s)
C) sF(s)
D) F(s)/s
🟢 Correct Answer: A) −F′(s)
🟡 Multiplication by t Property
L{tf(t)} = −F′(s)
🔵 Step-by-Step Solution

Suppose:

F(s)=L{f(t)}

Differentiate F(s) with respect to s:

F′(s) = −L{tf(t)}

Therefore:

L{tf(t)}=−F′(s)
🔴 Final Result: L{tf(t)} = −F′(s)
Question 27
If L{f(t)} = F(s), find L{t²f(t)}.
A) F″(s)
B) F″(s)
C) −F′(s)
D) s²F(s)
🟢 Correct Answer: B) F″(s)
🟡 Formula
L{tnf(t)} = (−1)nF(n)(s)
🔵 Step-by-Step Solution

For n = 2:

L{t²f(t)} = (−1)²F″(s)

Since (−1)² = 1:

L{t²f(t)}=F″(s)
🔴 Final Result: F″(s)
Question 28
Find L{teat}.
A) 1/(s−a)
B) 1/(s−a)²
C) 1/(s+a)²
D) s/(s−a)
🟢 Correct Answer: B)
🟡 Formula
L{teat} = 1 (s−a)²
🔵 Step-by-Step Solution

We know:

L{eat} = 1 s−a

Therefore:

F(s)= 1 s−a

Differentiate:

F′(s)= − 1 (s−a)²

Since L{tf(t)} = −F′(s):

L{teat} = 1 (s−a)²
🔴 Final Result: 1/(s−a)²
Question 29
Find L{t sin(at)}.
A) a/(s²+a²)
B) 2as/(s²+a²)²
C) s/(s²+a²)²
D) a²/(s²+a²)
🟢 Correct Answer: B)
🟡 Formula
L{sin(at)} = a s²+a²
🔵 Step-by-Step Solution

Let:

F(s)= a s²+a²

Differentiate with respect to s:

F′(s) = − 2as (s²+a²)²

Using L{tf(t)} = −F′(s):

L{t sin(at)} = 2as (s²+a²)²
🔴 Final Result: 2as/(s²+a²)²
Question 30
Find L{t cos(at)}.
A) a/(s²+a²)
B) s/(s²+a²)
C) (s²−a²)/(s²+a²)²
D) 2as/(s²+a²)²
🟢 Correct Answer: C)
🔵 Step-by-Step Solution

We know:

L{cos(at)} = s s²+a²

Differentiate:

F′(s) = a²−s² (s²+a²)²

Therefore:

−F′(s) = s²−a² (s²+a²)²

Hence:

L{t cos(at)} = s²−a² (s²+a²)²
🔴 Final Result: (s²−a²)/(s²+a²)²
Question 31
Find L{eatf(t)} if L{f(t)} = F(s).
A) F(s−a)
B) F(s+a)
C) aF(s)
D) F(as)
🟢 Correct Answer: A) F(s−a)
🟡 First Shifting Property
L{eatf(t)}=F(s−a)
🔵 Explanation

Multiplying f(t) by eat shifts the s-variable.

s → s−a

Therefore:

L{eatf(t)}=F(s−a)
🔴 Final Result: F(s−a)
Question 32
If L{f(t)} = F(s), find L{e−atf(t)}.
A) F(s−a)
B) F(s+a)
C) F(s−a²)
D) aF(s)
🟢 Correct Answer: B) F(s+a)
🔵 Step-by-Step Solution

Use:

L{eatf(t)}=F(s−a)

Replace a by −a:

F[s−(−a)]

Therefore:

L{e−atf(t)}=F(s+a)
🔴 Final Result: F(s+a)
Question 33
Find L{te2t}.
A) 1/(s−2)
B) 1/(s−2)²
C) 1/(s+2)²
D) 2/(s−2)
🟢 Correct Answer: B)
🔵 Step-by-Step Solution

Using the standard result:

L{teat} = 1 (s−a)²

Here a = 2:

L{te2t} = 1 (s−2)²
🔴 Final Result: 1/(s−2)²
Question 34
Find L{t²eat}.
A) 1/(s−a)²
B) 2/(s−a)³
C) 2/(s+a)³
D) 6/(s−a)²
🟢 Correct Answer: B)
🟡 Formula
L{t²eat} = 2 (s−a)³
🔵 Step-by-Step Solution

The general result is:

L{tneat} = n! (s−a)n+1

For n = 2:

L{t²eat} = 2! (s−a)³

Since 2! = 2:

= 2 (s−a)³
🔴 Final Result: 2/(s−a)³
Question 35
Find L{t³eat}.
A) 3/(s−a)⁴
B) 6/(s−a)⁴
C) 6/(s+a)⁴
D) 24/(s−a)³
🟢 Correct Answer: B)
🔵 Step-by-Step Solution
L{t³eat} = 3! (s−a)⁴

Since:

3!=6

Therefore:

L{t³eat} = 6 (s−a)⁴
🔴 Final Result: 6/(s−a)⁴
Question 36
Find L{t⁴eat}.
A) 4/(s−a)⁵
B) 24/(s−a)⁵
C) 12/(s−a)⁴
D) 24/(s−a)⁴
🟢 Correct Answer: B)
🔵 Step-by-Step Solution
L{t⁴eat} = 4! (s−a)⁵
4!=24
L{t⁴eat} = 24 (s−a)⁵
🔴 Final Result: 24/(s−a)⁵
Question 37
Find L{e2t sin(3t)}.
A) 3/(s²+9)
B) 3/[(s−2)²+9]
C) 2/[(s−3)²+4]
D) s/[(s−2)²+9]
🟢 Correct Answer: B)
🟡 Shifting Property
L{eatf(t)}=F(s−a)
🔵 Step-by-Step Solution

We know:

L{sin(3t)} = 3 s²+9

Here a = 2, so replace s by s−2:

L{e2tsin(3t)} = 3 (s−2)²+9
🔴 Final Result: 3/[(s−2)²+9]
Question 38
Find L{e2t cos(3t)}.
A) 3/[(s−2)²+9]
B) (s−2)/[(s−2)²+9]
C) s/(s²+9)
D) 2/[(s−3)²+4]
🟢 Correct Answer: B)
🔵 Step-by-Step Solution

We know:

L{cos(3t)} = s s²+9

Apply the exponential shifting property:

s → s−2

Therefore:

L{e2tcos(3t)} = s−2 (s−2)²+9
🔴 Final Result: (s−2)/[(s−2)²+9]
Question 39
Find L{e−3tsin(2t)}.
A) 2/[(s−3)²+4]
B) 2/[(s+3)²+4]
C) s/[(s+3)²+4]
D) 3/[(s+2)²+9]
🟢 Correct Answer: B)
🔵 Step-by-Step Solution

Start with:

L{sin(2t)} = 2 s²+4

Since the exponential is e−3t, replace s by s+3:

L{e−3tsin(2t)} = 2 (s+3)²+4
🔴 Final Result: 2/[(s+3)²+4]
Question 40
Find L{e−2tcos(4t)}.
A) (s−2)/[(s−2)²+16]
B) (s+2)/[(s+2)²+16]
C) 4/[(s+2)²+16]
D) s/(s²+16)
🟢 Correct Answer: B)
🔵 Step-by-Step Solution

We know:

L{cos(4t)} = s s²+16

Because of e−2t, replace s by s+2:

L{e−2tcos(4t)} = s+2 (s+2)²+16
🔴 Final Result: (s+2)/[(s+2)²+16]
🟣 Part 4 — Inverse Laplace Transform
Question 41
Find the inverse Laplace transform of 1/s.
A) 1
B) t
C) et
D) 0
🟢 Correct Answer: A) 1
🟡 Standard Pair
L{1} = 1 s
🔵 Solution

Since:

L{1}=1/s

Taking inverse Laplace transform:

L−1{1/s}=1
🔴 Final Answer: 1
Question 42
Find L−1{1/s²}.
A) 1
B) t
C) t²
D) et
🟢 Correct Answer: B) t
🔵 Step-by-Step Solution

We know:

L{t} = 1

Therefore:

L−1 { 1 } =t
🔴 Final Answer: t
Question 43
Find L−1{2/s³}.
A) t
B) t²
C) 2t
D) t³
🟢 Correct Answer: B) t²
🔵 Step-by-Step Solution

We know:

L{t²} = 2

Therefore:

L−1 { 2 } =t²
🔴 Final Answer: t²
Question 44
Find L−1{6/s⁴}.
A) t²
B) t³
C) 6t³
D) t⁴
🟢 Correct Answer: B) t³
🔵 Step-by-Step Solution

Using:

L{t³} = 6 s⁴

Therefore:

L−1 { 6 s⁴ } =t³
🔴 Final Answer: t³
Question 45
Find L−1{1/(s−a)}.
A) e−at
B) eat
C) aeat
D) est
🟢 Correct Answer: B) eat
🟡 Standard Pair
L{eat} = 1 s−a
🔵 Solution

Comparing with the standard transform pair:

1 s−a ↔ eat

Hence:

L−1 { 1 s−a } = eat
🔴 Final Answer: eat
Question 46
Find L−1{1/(s+a)}.
A) e−at
B) eat
C) ae−at
D) 1
🟢 Correct Answer: A) e−at
🔵 Step-by-Step Solution

We know:

L{e−at} = 1 s+a

Therefore:

L−1 { 1 s+a } = e−at
🔴 Final Answer: e−at
Question 47
Find L−1{a/(s²+a²)}.
A) sin(at)
B) cos(at)
C) sinh(at)
D) eat
🟢 Correct Answer: A) sin(at)
🟡 Standard Pair
L{sin(at)} = a s²+a²
🔵 Solution

Compare the given expression with the standard transform:

a s²+a² ↔ sin(at)

Hence:

L−1 { a s²+a² } = sin(at)
🔴 Final Answer: sin(at)
Question 48
Find L−1{s/(s²+a²)}.
A) sin(at)
B) cos(at)
C) sinh(at)
D) cosh(at)
🟢 Correct Answer: B) cos(at)
🔵 Step-by-Step Solution
L{cos(at)} = s s²+a²

Therefore:

L−1 { s s²+a² } = cos(at)
🔴 Final Answer: cos(at)
Question 49
Find L−1{a/(s²−a²)}.
A) sin(at)
B) cos(at)
C) sinh(at)
D) cosh(at)
🟢 Correct Answer: C) sinh(at)
🟡 Standard Pair
L{sinh(at)} = a s²−a²
🔵 Solution

Compare the expression:

a s²−a²

with the standard Laplace transform of sinh(at).

L−1 { a s²−a² } = sinh(at)
🔴 Final Answer: sinh(at)
Question 50
Find L−1{s/(s²−a²)}.
A) sinh(at)
B) sin(at)
C) cosh(at)
D) cos(at)
🟢 Correct Answer: C) cosh(at)
🟡 Standard Pair
L{cosh(at)} = s s²−a²
🔵 Step-by-Step Solution

Compare the given expression with:

L{cosh(at)} = s s²−a²

Therefore:

L−1 { s s²−a² } = cosh(at)
🔴 Final Answer: cosh(at)
Laplace Transform MCQs Q51-Q100

🔵 Laplace Transform MCQs

Q51–Q100 • Detailed Solutions

📘 Mathematics 🧠 Detailed Explanation 🎯 50 MCQs ➗ Proper Fractions
🟣 Part 5 — Partial Fractions & Inverse Laplace
Question 51
Find the inverse Laplace transform of 1 s(s+1) .
A) 1−e−t
B) 1−e−t
C) et−1
D) e−t
🟢 Correct Answer: B) 1−e−t
🔵 Step-by-Step Solution

Use partial fractions:

1 s(s+1) = A s + B s+1

Putting s = 0 gives A = 1.

Putting s = −1 gives B = −1.

= 1 s 1 s+1

Taking inverse Laplace:

1−e−t
🔴 Final Answer: 1−e−t
Question 52
Find L−1{ 1 s(s+2) }.
A) 1/2 − (1/2)e−2t
B) 1−e−2t
C) e−2t
D) 2−e−t
🟢 Correct Answer: A)
🔵 Solution
1 s(s+2) = 1/2 s 1/2 s+2

Taking inverse Laplace:

= 1 2 1 2 e−2t
🔴 Final Answer: (1/2)(1−e−2t)
Question 53
Find L−1{ 1 s(s+3) }.
A) 1−e−3t
B) 1/3 − (1/3)e−3t
C) 3−e−t
D) e−3t
🟢 Correct Answer: B)
🔵 Solution
1 s(s+3) = 1/3 s 1/3 s+3

Therefore:

L−1 = 1 3 1 3 e−3t
🔴 Final Answer: (1/3)(1−e−3t)
Question 54
Find L−1{ 2s+3 s²+3s+2 }.
A) 2e−t+e−2t
B) e−t+e−2t
C) 2et−e−2t
D) e−t−e−2t
🟢 Correct Answer: B)
🔵 Solution

Factor the denominator:

s²+3s+2=(s+1)(s+2)

Write:

2s+3 (s+1)(s+2) = A s+1 + B s+2

Solving gives A = 1 and B = 1.

Hence:

e−t+e−2t
🔴 Final Answer: e−t+e−2t
Question 55
Find L−1{ 1 (s+1)(s+2) }.
A) e−t+e−2t
B) e−t−e−2t
C) et−e2t
D) 1−e−t
🟢 Correct Answer: B)
🔵 Solution
1 (s+1)(s+2) = 1 s+1 1 s+2

Taking inverse Laplace:

e−t−e−2t
🔴 Final Answer: e−t−e−2t
Question 56
Find L−1{ s s²+4 }.
A) sin 2t
B) cos 2t
C) 2sin 2t
D) e−2t
🟢 Correct Answer: B) cos 2t
🔵 Solution

Compare with:

L{cos(at)} = s s²+a²

Here a² = 4, so a = 2.

L−1 { s s²+4 } = cos(2t)
🔴 Final Answer: cos 2t
Question 57
Find L−1{ 2 s²+4 }.
A) sin 2t
B) cos 2t
C) 2sin t
D) cos t
🟢 Correct Answer: A) sin 2t
🔵 Solution
L{sin(at)} = a s²+a²

For a = 2:

L{sin(2t)} = 2 s²+4

Hence the inverse is sin(2t).

🔴 Final Answer: sin 2t
Question 58
Find L−1{ 3 s²+9 }.
A) cos 3t
B) sin 3t
C) 3cos t
D) e−3t
🟢 Correct Answer: B) sin 3t
🔵 Solution
L{sin(3t)} = 3 s²+9

Therefore:

L−1 { 3 s²+9 } = sin(3t)
🔴 Final Answer: sin 3t
Question 59
Find L−1{ s s²−9 }.
A) cos 3t
B) sin 3t
C) cosh 3t
D) sinh 3t
🟢 Correct Answer: C) cosh 3t
🔵 Solution

Use:

L{cosh(at)} = s s²−a²

Here a = 3.

L−1 { s s²−9 } = cosh(3t)
🔴 Final Answer: cosh 3t
Question 60
Find L−1{ 3 s²−9 }.
A) cosh 3t
B) sinh 3t
C) sin 3t
D) cos 3t
🟢 Correct Answer: B) sinh 3t
🔵 Solution
L{sinh(at)} = a s²−a²

Putting a = 3:

L{sinh(3t)} = 3 s²−9
🔴 Final Answer: sinh 3t
🟠 Part 6 — Advanced Inverse Laplace
Question 61
Find L−1{ 1 (s−2)² }.
A) te2t
B) e2t
C) 2tet
D) t²e2t
🟢 Correct Answer: A) te2t
🔵 Solution

Use:

L{teat} = 1 (s−a)²

For a = 2:

L−1 { 1 (s−2)² } = te2t
🔴 Final Answer: te2t
Question 62
Find L−1{ 2 (s−3)³ }.
A) te3t
B) t²e3t
C) 2t²e3t
D) e3t
🟢 Correct Answer: B) t²e3t
🔵 Solution

Use:

L{t²eat} = 2 (s−a)³

For a = 3:

L−1 { 2 (s−3)³ } = t²e3t
🔴 Final Answer: t²e3t
Question 63
Find L−1{ 6 (s+1)⁴ }.
A) t²e−t
B) t³e−t
C) 6t³e−t
D) te−t
🟢 Correct Answer: B) t³e−t
🔵 Solution

Use:

L{t³eat} = 6 (s−a)⁴

Here a = −1:

(s−a)=(s+1)

Therefore:

L−1 { 6 (s+1)⁴ } = t³e−t
🔴 Final Answer: t³e−t
Question 64
Find L−1{ s+2 (s+2)²+9 }.
A) sin 3t
B) e−2tcos 3t
C) e2tcos 3t
D) cos 2t
🟢 Correct Answer: B)
🔵 Solution

We know:

L{cos(3t)} = s s²+9

Apply the shifting rule with s replaced by s+2:

L{e−2tcos(3t)} = s+2 (s+2)²+9
🔴 Final Answer: e−2tcos 3t
Question 65
Find L−1{ 3 (s+2)²+9 }.
A) cos 3t
B) e−2tsin 3t
C) e2tsin 3t
D) sin 2t
🟢 Correct Answer: B)
🔵 Solution

Start with:

L{sin(3t)} = 3 s²+9

Replace s with s+2:

L{e−2tsin(3t)} = 3 (s+2)²+9
🔴 Final Answer: e−2tsin 3t
Question 66
Find L−1{ s−1 (s−1)²+4 }.
A) etcos 2t
B) e−tcos 2t
C) etsin 2t
D) cos t
🟢 Correct Answer: A)
🔵 Solution

The standard form is:

L{eatcos(bt)} = s−a (s−a)²+b²

Comparing:

a=1,\qquad b=2

Therefore:

L−1 = etcos(2t)
🔴 Final Answer: etcos 2t
Question 67
Find L−1{ 2 (s−1)²+4 }.
A) etcos 2t
B) etsin 2t
C) e−tsin 2t
D) sin t
🟢 Correct Answer: B)
🔵 Solution

Use:

L{eatsin(bt)} = b (s−a)²+b²

Here a = 1 and b = 2.

L{etsin(2t)} = 2 (s−1)²+4
🔴 Final Answer: etsin 2t
Question 68
Find L−1{ s+3 (s+3)²+16 }.
A) e3tcos 4t
B) e−3tcos 4t
C) e−3tsin 4t
D) cos 3t
🟢 Correct Answer: B)
🔵 Solution

Compare with:

s−a (s−a)²+b²

Here:

s−a=s+3

Therefore a = −3.

Also b² = 16, so b = 4.

L−1} = e−3tcos(4t)
🔴 Final Answer: e−3tcos 4t
Question 69
Find L−1{ 4 (s+3)²+16 }.
A) e3tsin 4t
B) e−3tsin 4t
C) e−4tsin 3t
D) cos 4t
🟢 Correct Answer: B)
🔵 Solution

Use:

L{eatsin(bt)} = b (s−a)²+b²

Here a = −3 and b = 4.

L−1 = e−3tsin(4t)
🔴 Final Answer: e−3tsin 4t
Question 70
Find L−1{ s+1 (s+1)²−9 }.
A) etcosh 3t
B) e−tcosh 3t
C) e−tsinh 3t
D) cosh t
🟢 Correct Answer: B)
🔵 Solution

Use:

L{eatcosh(bt)} = s−a (s−a)²−b²

Comparing:

s−a=s+1

Thus a = −1.

Also b = 3.

L−1 = e−tcosh(3t)
🔴 Final Answer: e−tcosh 3t
🟢 Part 7 — Laplace Transform Properties & Applications
Question 71
What is L{f(t) + g(t)}?
A) F(s)+G(s)
B) F(s)G(s)
C) F(s)−G(s)
D) F(s)/G(s)
🟢 Correct Answer: A) F(s)+G(s)
🔵 Explanation

The Laplace transform is linear:

L{f(t)+g(t)} = L{f(t)}+L{g(t)}

Therefore:

F(s)+G(s)
🔴 Final Answer: F(s)+G(s)
Question 72
What is L{af(t)}?
A) aF(s)
B) F(as)
C) F(s)/a
D) F(s)+a
🟢 Correct Answer: A) aF(s)
🔵 Solution

A constant multiplier can be taken outside the Laplace transform:

L{af(t)} = aL{f(t)}

Thus:

=aF(s)
🔴 Final Answer: aF(s)
Question 73
Find L{0}.
A) 1
B) 0
C) s
D) 1/s
🟢 Correct Answer: B) 0
🔵 Solution

Using the definition:

L{0} = ∫0 e−st(0)dt

The entire integrand is zero.

L{0}=0
🔴 Final Answer: 0
Question 74
Find L{tn}.
A) n!/sn
B) n!/sn+1
C) sn/n!
D) 1/s
🟢 Correct Answer: B)
🟡 Standard Formula
L{tn} = n! sn+1
🔵 Explanation

This is one of the fundamental Laplace transform formulas.

For example, n = 3:

L{t³} = 3! s⁴ = 6 s⁴
🔴 Final Result: n!/sn+1
Question 75
Find L{eat}.
A) 1/(s−a)
B) 1/(s+a)
C) a/(s−a)
D) s/(s−a)
🟢 Correct Answer: A)
🔵 Solution
L{eat} = ∫0 e−steatdt
= ∫0 e−(s−a)tdt
= 1 s−a
🔴 Final Answer: 1/(s−a)
Question 76
Find L{sin t}.
A) 1/(s²+1)
B) s/(s²+1)
C) 1/(s+1)
D) s/(s²−1)
🟢 Correct Answer: A)
🔵 Solution

Use:

L{sin(at)} = a s²+a²

For a = 1:

L{sin t} = 1 s²+1
🔴 Final Answer: 1/(s²+1)
Question 77
Find L{cos t}.
A) 1/(s²+1)
B) s/(s²+1)
C) 1/(s+1)
D) s/(s²−1)
🟢 Correct Answer: B)
🔵 Solution
L{cos(at)} = s s²+a²

Put a = 1:

L{cos t} = s s²+1
🔴 Final Answer: s/(s²+1)
Question 78
Find L{sinh t}.
A) 1/(s²+1)
B) 1/(s²−1)
C) s/(s²−1)
D) 1/(s+1)
🟢 Correct Answer: B)
🔵 Solution

Use:

L{sinh(at)} = a s²−a²

For a = 1:

L{sinh t} = 1 s²−1
🔴 Final Answer: 1/(s²−1)
Question 79
Find L{cosh t}.
A) 1/(s²+1)
B) 1/(s²−1)
C) s/(s²−1)
D) s/(s²+1)
🟢 Correct Answer: C)
🔵 Solution
L{cosh(at)} = s s²−a²

For a = 1:

L{cosh t} = s s²−1
🔴 Final Answer: s/(s²−1)
Question 80
Find L{t e−t}.
A) 1/(s−1)²
B) 1/(s+1)²
C) 1/(s+1)
D) 2/(s+1)³
🟢 Correct Answer: B)
🔵 Solution

Use:

L{teat} = 1 (s−a)²

Here a = −1:

s−a=s+1

Therefore:

L{te−t} = 1 (s+1)²
🔴 Final Answer: 1/(s+1)²
🔴 Part 8 — Mixed & Exam-Level Questions
Question 81
Find the Laplace transform of 2t + 3.
A) 2/s² + 3/s
B) 2/s + 3/s²
C) 5/s²
D) 2s+3
🟢 Correct Answer: A)
🔵 Solution
L{2t+3} = 2L{t}+3L{1}
= 2 + 3 s
🔴 Final Answer: 2/s² + 3/s
Question 82
Find L{3t² + 2t + 1}.
A) 6/s³ + 2/s² + 1/s
B) 3/s³ + 2/s² + 1/s
C) 6/s² + 2/s + 1
D) 3/s² + 2/s + 1/s
🟢 Correct Answer: A)
🔵 Solution
L{3t²+2t+1} = 3L{t²}+2L{t}+L{1}
= 3 2 + 2 1 + 1 s
= 6 + 2 + 1 s
🔴 Final Answer: 6/s³ + 2/s² + 1/s
Question 83
Find L{e2t}.
A) 1/(s+2)
B) 1/(s−2)
C) 2/(s−1)
D) s/(s−2)
🟢 Correct Answer: B)
🔵 Solution
L{eat} = 1 s−a

Putting a = 2:

L{e2t} = 1 s−2
🔴 Final Answer: 1/(s−2)
Question 84
Find L{4e−2t}.
A) 4/(s+2)
B) 4/(s−2)
C) 2/(s+4)
D) 1/(s+2)
🟢 Correct Answer: A)
🔵 Solution
L{e−2t} = 1 s+2

Multiplying by 4:

L{4e−2t} = 4 s+2
🔴 Final Answer: 4/(s+2)
Question 85
Find L{2sin(3t)+4cos(3t)}.
A) 6/(s²+9)+4s/(s²+9)
B) 6/(s²+9)+4s/(s²+9)
C) 2/(s²+9)+12s/(s²+9)
D) 6s/(s²+9)+4/(s²+9)
🟢 Correct Answer: B)
🔵 Solution

Use linearity:

L{2sin(3t)} = 6 s²+9
L{4cos(3t)} = 4s s²+9

Therefore:

L = 6+4s s²+9
🔴 Final Result: (4s+6)/(s²+9)
Question 86
Find L{3sinh(2t)}.
A) 6/(s²−4)
B) 3/(s²−4)
C) 6/(s²+4)
D) 2/(s²−9)
🟢 Correct Answer: A)
🔵 Solution
L{sinh(2t)} = 2 s²−4

Multiply by 3:

L{3sinh(2t)} = 6 s²−4
🔴 Final Answer: 6/(s²−4)
Question 87
Find L{5cosh(2t)}.
A) 10/(s²−4)
B) 5s/(s²−4)
C) 5s/(s²+4)
D) 2s/(s²−5)
🟢 Correct Answer: B)
🔵 Solution
L{cosh(2t)} = s s²−4

Multiply by 5:

L{5cosh(2t)} = 5s s²−4
🔴 Final Answer: 5s/(s²−4)
Question 88
Find L{t²}.
A) 1/s²
B) 2/s³
C) 2/s²
D) 6/s³
🟢 Correct Answer: B)
🔵 Solution
L{t²} = 2!
2!=2
L{t²} = 2
🔴 Final Answer: 2/s³
Question 89
Find L{t⁵}.
A) 24/s⁵
B) 120/s⁶
C) 60/s⁵
D) 120/s⁵
🟢 Correct Answer: B)
🔵 Solution
L{t⁵} = 5! s⁶

Now:

5!=5×4×3×2×1=120

Therefore:

L{t⁵} = 120 s⁶
🔴 Final Answer: 120/s⁶
Question 90
Find L{t⁶}.
A) 120/s⁶
B) 720/s⁷
C) 720/s⁶
D) 360/s⁷
🟢 Correct Answer: B)
🔵 Solution
L{t⁶} = 6! s⁷
6!=720
L{t⁶} = 720 s⁷
🔴 Final Answer: 720/s⁷
Question 91
If L{f(t)} = F(s), then L{f(t)/t} is related to:
A) F′(s)
B) ∫sF(u)du
C) sF(s)
D) F(s)/s
🟢 Correct Answer: B)
🟡 Division by t Property
L{ f(t) t } = ∫sF(u)du
🔵 Explanation

A standard Laplace property states:

L{ f(t) t } = ∫sF(u)du

This property is useful when the time-domain function is divided by t.

🔴 Final Result: ∫sF(u)du
Question 92
What is the Laplace transform of a derivative mainly useful for?
A) Solving differential equations
B) Finding only factorials
C) Finding only trigonometric values
D) Measuring angles
🟢 Correct Answer: A) Solving differential equations
🔵 Explanation

The derivative property converts derivatives in the time domain into algebraic expressions involving s in the Laplace domain.

L{f′(t)} = sF(s)−f(0)

This conversion makes many differential equations easier to solve algebraically.

🔴 Final Answer: Solving differential equations
Question 93
Find L{f′(t)} when F(s)=1/s and f(0)=1.
A) s−1
B) 0
C) 1/s²
D) s
🟢 Correct Answer: B) 0
🔵 Solution

Use:

L{f′(t)} = sF(s)−f(0)

Given:

F(s)= 1 s

and f(0)=1.

L{f′(t)} = s 1 s −1
=1−1=0
🔴 Final Answer: 0
Question 94
If f(0)=3 and F(s)=2/s, find L{f′(t)}.
A) −1
B) 1
C) 2s−3
D) 3s−2
🟢 Correct Answer: A) −1
🔵 Solution
L{f′(t)} = sF(s)−f(0)

Substitute:

= s 2 s −3
=2−3
=-1
🔴 Final Answer: −1
Question 95
Find L−1{ 1 s²(s+1) }.
A) t+e−t
B) t−1+e−t
C) 1−te−t
D) t+1−e−t
🟢 Correct Answer: B)
🔵 Step-by-Step Solution

Use partial fractions:

1 s²(s+1) = A s + B + C s+1

Solving the coefficients gives:

A=−1,\qquad B=1,\qquad C=1

Therefore:

1 s + 1 + 1 s+1

Taking inverse Laplace:

−1+t+e−t
🔴 Final Answer: t−1+e−t
Question 96
Find L−1{ s+4 s²+4s+13 }.
A) e−2tcos 3t + (2/3)e−2tsin 3t
B) e2tcos 3t
C) e−2tsin 3t
D) cos 3t
🟢 Correct Answer: A)
🔵 Step-by-Step Solution

Complete the square:

s²+4s+13 = (s+2)²+9

Rewrite the numerator:

s+4=(s+2)+2

Therefore:

s+4 (s+2)²+9 = s+2 (s+2)²+9 + 2 (s+2)²+9

Now:

L−1 { s+2 (s+2)²+9 } = e−2tcos3t

Also:

L−1 { 2 (s+2)²+9 } = 2 3 e−2tsin3t
🔴 Final Answer: e−2tcos3t + (2/3)e−2tsin3t
Question 97
Find L{t cosh(at)}.
A) (s²+a²)/(s²−a²)²
B) (s²+a²)/(s²−a²)²
C) 2as/(s²−a²)²
D) s/(s²−a²)
🟢 Correct Answer: B)
🔵 Step-by-Step Solution

We know:

L{cosh(at)} = s s²−a²

Let:

F(s)= s s²−a²

Differentiate:

F′(s) = −(s²+a²) (s²−a²)²

Using L{tf(t)} = −F′(s):

L{t cosh(at)} = s²+a² (s²−a²)²
🔴 Final Answer: (s²+a²)/(s²−a²)²
Question 98
Find L{t sinh(at)}.
A) (a²−s²)/(s²−a²)²
B) −(s²+a²)/(s²−a²)²
C) 2as/(s²−a²)²
D) a/(s²−a²)
🟢 Correct Answer: B)
🔵 Step-by-Step Solution

We know:

L{sinh(at)} = a s²−a²

Differentiate with respect to s:

F′(s) = −2as (s²−a²)²

Hence:

L{t sinh(at)} = 2as (s²−a²)²

Therefore the correct expression is:

2as (s²−a²)²
🔴 Final Result: 2as/(s²−a²)²
Question 99
Find L{t sin(2t)}.
A) 2/(s²+4)
B) 4s/(s²+4)²
C) 2s/(s²+4)²
D) 4/(s²+4)
🟢 Correct Answer: B)
🔵 Step-by-Step Solution

Start with:

L{sin(2t)} = 2 s²+4

Differentiate:

F′(s) = − 4s (s²+4)²

Since:

L{tf(t)}=−F′(s)

we get:

L{t sin(2t)} = 4s (s²+4)²
🔴 Final Answer: 4s/(s²+4)²
Question 100
Which statement correctly represents the Laplace transform of a second derivative?
A) L{f”(t)} = sF(s)
B) L{f”(t)} = s²F(s)−sf(0)−f'(0)
C) L{f”(t)} = F(s)/s²
D) L{f”(t)} = F′(s)
🟢 Correct Answer: B)
🟡 Important Formula
L{f”(t)} = s²F(s)−sf(0)−f′(0)
🔵 Detailed Explanation

First derivative:

L{f′(t)} = sF(s)−f(0)

Apply the derivative property once more:

L{f”(t)} = sL{f′(t)}−f′(0)

Substitute the first derivative result:

= s[sF(s)−f(0)]−f′(0)

Expand:

= s²F(s)−sf(0)−f′(0)

This formula is especially important when solving second-order differential equations using Laplace transforms.

🔴 Final Answer: s²F(s)−sf(0)−f′(0)

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top