Kinetic Energy — JEE Main Physics MCQs with Solutions
Free JEE Main Physics Kinetic Energy MCQs with step-by-step solutions (8 questions). Part of Work, Power and Energy. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Kinetic Energy · easy · theory
Kinetic energy in terms of the momentum p and mass m is:
A. KE = 2m/p²
B. KE = p²/2m ✓ Correct
C. KE = p²m/2
D. KE = p/2m
Solution: KE = ½mv² and p = mv give KE = p²/2m. KE is a scalar and can never be negative.
Q2 — Kinetic Energy · medium · theory
If the momentum of a body is doubled, its kinetic energy becomes:
A. Unchanged
B. 4 times ✓ Correct
C. √2 times
D. 2 times
Solution: KE = p²/2m ∝ p². Doubling p quadruples KE. Trap: doubling KE only raises p by √2.
Q3 — Kinetic Energy · easy · numerical
A 2 kg body moves at 10 m/s. Its kinetic energy is:
A. 50 J
B. 200 J
C. 20 J
D. 100 J ✓ Correct
Solution: KE = ½mv² = ½×2×100 = 100 J.
Q4 — Kinetic Energy · medium · numerical
A body of mass 5 kg has momentum 10 kg·m/s. Its kinetic energy is:
A. 5 J
B. 10 J ✓ Correct
C. 50 J
D. 20 J
Solution: KE = p²/2m = 100/10 = 10 J.
Q5 — Kinetic Energy · hard · numerical
The kinetic energy of a body is increased by 300%. The percentage increase in its momentum is:
A. 200%
B. 100% ✓ Correct
C. 73%
D. 300%
Solution: New KE = 4×old ⇒ p ∝ √KE doubles ⇒ +100%. Trap: 300% increase means ×4, not ×3.
Q6 — Kinetic Energy · medium · numerical
Two bodies of masses 1 kg and 4 kg have equal kinetic energies. The ratio of their momenta p₁ : p₂ is:
A. 2 : 1
B. 1 : 16
C. 1 : 2 ✓ Correct
D. 1 : 4
Solution: p = √(2m·KE) ∝ √m for equal KE ⇒ p₁:p₂ = 1:2.
Q7 — Kinetic Energy · medium · numerical
Two bodies with masses in the ratio 1 : 2 have equal momenta. The ratio of their kinetic energies KE₁ : KE₂ is:
A. 1 : 2
B. 1 : 4
C. 2 : 1 ✓ Correct
D. 4 : 1
Solution: KE = p²/2m ∝ 1/m for equal p ⇒ the lighter body has twice the KE: 2:1.
Q8 — Kinetic Energy · hard · numerical
The kinetic energy of a particle decreases by 19%. The percentage decrease in its momentum is:
A. 9.5%
B. 19%
C. 10% ✓ Correct
D. 81%
Solution: KE becomes 0.81× ⇒ p ∝ √KE becomes 0.9× ⇒ 10% decrease.