Exams › JEE Main › Physics

A lift is descending with acceleration a. A person inside the lift releases a ball from rest. The acceleration of the ball as measured by the person in the lift and by an observer standing on the ground are, respectively,

1. g, g
2. g − a, g − a
3. g − a, g
4. a, g

Correct answer: g − a, g

Solution

The person inside the lift experiences a reduced effective gravitational acceleration due to the downward acceleration of the lift, resulting in the ball accelerating at g - a relative to them. However, an observer on the ground sees the ball accelerating at the full gravitational acceleration g, as they are not affected by the lift's motion.

Related JEE Main Physics questions

• A thief is escaping along a straight road in a jeep traveling at 9 m/s. A policeman follows him on a motorcycle moving at 10 m/s. If the current distance between the jeep and the motorcycle is 100 m, after how much time will the policeman catch the thief?
• A metro train begins from rest and reaches a speed of 108 km/h in 5 s. It then continues at this constant speed and finally is brought to rest by a uniform retardation over a distance of 45 m. If the entire journey covers 395 m, what is the total time taken?
• A motor boat is moving with speed v0 when its engine is switched off. Its deceleration is described by dv/dt = −kv³, where k is a constant. The speed of the boat after time t from the moment of cut-off is
• From the top of a 100 m tall tower, one ball is released from rest. At the same instant, another ball is thrown straight upward from the ground with speed 25 m s^−1. How far below the top of the tower do the two balls meet?
• A particle moves with velocity given by v = v0 + gt + ft². If its position is x = 0 at t = 0, what is its displacement at t = 1?
• A car travelling at 50 km/h can be brought to rest by applying the brakes over a minimum distance of 6 m. If the same car is moving at 100 km/h, what is the least distance needed to stop it?

⚔️ Practice JEE Main Physics free + battle 1v1 →