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JEE Physics

Physics questions for JEE Main — Mechanics, Electrostatics, Optics, Modern Physics.

434 Q 9 Topics Take Test
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Difficulty: All Easy Medium Hard 421–430 of 434
Topics in JEE Physics
Q.421 Medium Mechanics
A ball is dropped from height h and bounces back to height h/2 after first bounce. What is the coefficient of restitution?
A 0.5
B 0.707
C 0.866
D 1
Correct Answer:  B. 0.707
EXPLANATION

e = √(h₂/h₁) = √(h/2 ÷ h) = √(1/2) ≈ 0.707

Test
Q.422 Medium Mechanics
A mass of 2 kg is attached to a spring with constant k = 50 N/m. The system oscillates with amplitude 0.1 m. What is the maximum velocity?
A 0.5 m/s
B 1 m/s
C 1.5 m/s
D 2 m/s
Correct Answer:  A. 0.5 m/s
EXPLANATION

For SHM, ωmax = ω × A where ω = √(k/m) = √(50/2) = 5 rad/s. vmax = 5 × 0.1 = 0.5 m/s

Test
Q.423 Medium Mechanics
A block is pushed up an incline of angle 30° with initial velocity 10 m/s. If coefficient of kinetic friction is 0.2, how far will it travel before stopping? (g = 10 m/s²)
A 3.2 m
B 4.5 m
C 5.2 m
D 6.8 m
Correct Answer:  A. 3.2 m
EXPLANATION

Deceleration a = g(sinθ + μcosθ) = 10(0.5 + 0.2×0.866) = 10(0.5 + 0.173) = 6.73 m/s². Using v² = u² - 2as: 0 = 100 - 2(6.73)s, s ≈ 3.2 m

Test
Q.424 Medium Mechanics
Two objects A and B are thrown vertically upward with same initial velocity from the ground. If A is thrown 1 second before B, when will they have the same velocity?
A 0.5 s after B is thrown
B 1 s after B is thrown
C Never
D At the moment B is thrown
Correct Answer:  C. Never
EXPLANATION

Both objects have constant acceleration -g. If thrown with same initial velocity but at different times, they will have the same velocity at different times. For same velocity at same instant: vA = u - gt₁ and vB = u - gt₂. Since t₁ ≠ t₂, velocities won't be equal at the same instant.

Test
Q.425 Medium Mechanics
A particle moves in a straight line with acceleration a = 3t² m/s². If initial velocity is 2 m/s, find velocity after 2 seconds.
A 10 m/s
B 12 m/s
C 14 m/s
D 16 m/s
Correct Answer:  A. 10 m/s
EXPLANATION

v = u + ∫a dt = 2 + ∫₀² 3t² dt = 2 + [t³]₀² = 2 + 8 = 10 m/s

Test
Q.426 Medium Mechanics
A particle has position x = 4t² - 2t + 3. Its velocity at t = 1s is:
A 4 m/s
B 6 m/s
C 8 m/s
D 10 m/s
Correct Answer:  B. 6 m/s
EXPLANATION

v = dx/dt = 8t - 2. At t = 1s, v = 8(1) - 2 = 6 m/s

Test
Q.427 Medium Mechanics
Work done by centripetal force in circular motion is:
A Positive
B Negative
C Zero
D Depends on radius
Correct Answer:  C. Zero
EXPLANATION

Centripetal force is perpendicular to velocity (displacement), so W = F·s·cosθ = F·s·cos90° = 0

Test
Q.428 Medium Mechanics
A 50 kg person stands in an elevator accelerating upward at 2 m/s². Normal force is: (g = 10 m/s²)
A 400 N
B 500 N
C 600 N
D 700 N
Correct Answer:  C. 600 N
EXPLANATION

N - mg = ma. N = m(g+a) = 50(10+2) = 600 N

Test
Q.429 Medium Mechanics
A ball thrown upward returns to same height in 4s. Initial velocity is: (g = 10 m/s²)
A 10 m/s
B 15 m/s
C 20 m/s
D 25 m/s
Correct Answer:  C. 20 m/s
EXPLANATION

Time to max height = 2s. u = gt = 10(2) = 20 m/s

Test
Q.430 Medium Mechanics
Two blocks (m₁ = 3 kg, m₂ = 2 kg) are connected by a string on a frictionless surface. Applied force F = 20 N. Tension in string is:
A 8 N
B 10 N
C 12 N
D 15 N
Correct Answer:  A. 8 N
EXPLANATION

System acceleration: a = F/(m₁+m₂) = 20/5 = 4 m/s². Tension = m₂a = 2(4) = 8 N

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