A boy standing at the top of a tower of 20 m height drops a stone. Assuming g = 10 m s^$$-$$2, the velocity with which it hits the ground is

A ball is dropped from a high rise platform at t = 0 starting from rest. After 6 seconds another ball is thrown downwards from the same platform with a speed v. The two balls meet at t = 18 s. What is the value of v?
(Take g = 10 m/s²)

A particle moves a distance x in time t according to equation x = (t + 5)^$$-$$1. The acceleration of particle is proportional to

A bus is moving with a speed of 10 ms^$$-$$1 on a straight road. A scooterist wishes to overtake the bus in 100 s. If the bus is at a distance of 1 km from the scooterist, with what speed should the scooterist chase the bus ?