A car moving with speed 54 km/h is stopped in 5 s. The distance covered before stop is MCQ with Answer and Explanation

A car moving with speed 54 km/h is stopped in 5 s. The distance covered before stop is

A. 37.5 m

B. 54 m

C. 27 m

D. 75 m

Answer: Option A

Solution (By JKExamLibrary)

54 km/h = 15 m/s. u=15, v=0, t=5. a = (0-15)/5 = -3 m/s². s = ut+½at² = 15×5 + ½×(-3)×25 = 75 - 37.5 = 37.5 m. Or s = (u+v)/2 × t = 7.5×5 = 37.5 m.

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Two waves of identical frequency and amplitude superimpose in the same medium. If they meet perfectly in phase (crest meets crest), the resulting amplitude is:

A. Four times the individual amplitude

B. Twice the individual amplitude

C. Zero

D. Same as the individual amplitude

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Correct Answer: Option B

Explanation:
This is an example of constructive interference. According to the principle of superposition, the resultant displacement is the algebraic sum of individual displacements. If the waves are perfectly in phase, their amplitudes add directly (A + A = 2A). Note that while amplitude doubles, the intensity (which is proportional to amplitude squared) becomes four times greater.

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Question #2 Report Error

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B. R

C. R/2

D. 4R

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Correct Answer: Option D

Explanation:
R ∝ L/A. New L'=2L, A'=A/2 => R' = ρ(2L)/(A/2) = 4ρL/A = 4R. Alternatively, volume constant? Not given, here both changed independently. So 4R.

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Two objects of masses 1 kg and 4 kg have equal momentum. What is the ratio of their kinetic energies?

A. 4:1

B. 1:4

C. 1:2

D. 2:1

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Correct Answer: Option A

Explanation:
Kinetic Energy (K) is related to momentum (p) by the formula K = p² / 2m. Since they have equal momentum, p is constant. Therefore, K is inversely proportional to mass (K ∝ 1/m). Ratio of kinetic energies K1/K2 = m2/m1 = 4/1 = 4:1. The lighter object has more kinetic energy.

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