Question Paper from: JEE Main 2021 - Paper 1

A body having a specific charge of $8 μ C / g$ is resting on a frictionless plane at a distance of 10 cm from the wall (as shown in the figure). It starts moving towards the wall when a uniform electric field of 100 V/m is applied horizontally towards the wall. If the collision of the body with the wall is perfectly elastic, the time period of the motion will be _______s.

Correct Answer :

Solution:

Chapter Name: Collision

Difficulty Level: Difficulty

$a = \frac{qE}{m} = \frac{8 \times 1 0 ^{- 6}}{1 0 ^{- 3}} \times 100 = 0.8 m / s^{2}$

As the electric field is switched on, the ball first strikes the wall and returns back. one oscillation.

Thus $s = u t_{1} + \frac{1}{2} a t_{1}^{2}$

$0.1 = \frac{1}{2} \times 0.8 t_{1}^{2}; t_{1} = \frac{1}{2} s$

Thus time period T $= 2 \times \frac{1}{2} = 1 sec$

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