Two objects of equal mass collide elastically and exchange velocities. This is possible only if:

The correct answer is A: One object was at rest before collision. In elastic collision between equal masses, if one is at rest, they exchange velocities completely. This satisfies both momentum and energy conservation.

A hydrogen atom transitions from n=4 to n=2 state. The wavelength of emitted photon is approximately:

The correct answer is A: 486 nm. Using Rydberg formula: 1/λ = R(1/4 - 1/16) = 3R/16. With R = 1.097×10⁷ m⁻¹, we get λ ≈ 486 nm (H-beta line).

In a circuit, three resistors of 2Ω, 3Ω, and 6Ω are connected in parallel. The equivalent resistance is:

The correct answer is A: 1Ω. 1/R_eq = 1/2 + 1/3 + 1/6 = 3/6 + 2/6 + 1/6 = 6/6 = 1. Therefore R_eq = 1Ω

The critical angle for total internal reflection from a denser medium to air (n = 1) is 45°. What is the refractive index of the denser medium?

The correct answer is A: 1.41. At critical angle: sin(θc) = 1/n. So sin(45°) = 1/n gives 1/√2 = 1/n, therefore n = √2 ≈ 1.41.

The temperature coefficient of resistance for a conductor is positive. This means:

The correct answer is A: Resistance increases with temperature. Positive temperature coefficient means R = R₀(1 + αΔT) where α > 0, so resistance increases with increasing temperature

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Mechanics

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

50 Q 9 Topics Take Mock Test

Difficulty: All Easy Medium Hard 31–40 of 50

Topics in JEE Physics

All Mechanics 100 Thermodynamics 100 Electrostatics 100 Current Electricity 100 Magnetism 100 Optics 100 Modern Physics 100 Semiconductors 100 Waves 100

Q.31 Medium Mechanics

Two blocks A (2 kg) and B (3 kg) are connected by a string on a frictionless surface. A 10 N force pulls the system. The tension in the string between A and B is:

A 4 N

B 6 N

C 8 N

D 10 N

Correct Answer: B. 6 N

EXPLANATION

Total acceleration = F/(m₁+m₂) = 10/5 = 2 m/s². Tension = F - m₁a = 10 - 2×2 = 6 N (or T = m₂a = 3×2 = 6 N)

Test

Q.32 Medium Mechanics

A 2 kg block slides down a 30° incline with initial velocity 5 m/s. If friction coefficient is 0.1, what is acceleration? (g = 10 m/s²)

A 3.6 m/s²

B 4.3 m/s²

C 5.1 m/s²

D 6.2 m/s²

Correct Answer: B. 4.3 m/s²

EXPLANATION

a = g(sinθ - μcosθ) = 10(sin30° - 0.1×cos30°) = 10(0.5 - 0.1×0.866) = 10(0.5 - 0.0866) = 4.134 ≈ 4.3 m/s²

Test

Q.33 Medium Mechanics

A ball is thrown from ground with initial velocity components: vₓ = 20 m/s and vᵧ = 30 m/s. At maximum height, what is its velocity?

A 20 m/s

B 30 m/s

C 25 m/s

D 40 m/s

Correct Answer: A. 20 m/s

EXPLANATION

At maximum height, vertical component vᵧ = 0. Horizontal component vₓ remains 20 m/s. Total velocity = 20 m/s

Test

Q.34 Medium Mechanics

A satellite orbits Earth at radius r with velocity v. If radius is doubled, what is new orbital velocity?

A v

B v/√2

C v√2

D 2v

Correct Answer: B. v/√2

EXPLANATION

Orbital velocity v = √(GM/r). If r → 2r, then v' = √(GM/2r) = v/√2

Test

Q.35 Medium Mechanics

A particle in circular motion has angular velocity ω = 2t rad/s. If radius is 5 m, what is tangential acceleration at t = 2s?

A 5 m/s²

B 10 m/s²

C 15 m/s²

D 20 m/s²

Correct Answer: B. 10 m/s²

EXPLANATION

Tangential acceleration at = r(dω/dt) = 5 × 2 = 10 m/s² (constant as dω/dt = 2)

Test

Q.36 Medium Mechanics

Two objects of mass 4 kg and 6 kg move towards each other with velocities 5 m/s and 3 m/s respectively. After perfectly inelastic collision, what is their common velocity?

A 0.2 m/s

B 0.4 m/s

C 0.6 m/s

D 0.8 m/s

Correct Answer: A. 0.2 m/s

EXPLANATION

By momentum conservation: 4(5) - 6(3) = (4+6)v → 20 - 18 = 10v → v = 0.2 m/s

Test

Q.37 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.38 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.39 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.40 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.

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