Question

A stone thrown upward from the top of a tower 85m high reaches the ground in 5 second 1:-calculate the greatest height above the ground? 2:-the velocity with which it reaches the ground? 3:-the time taken to reach the aximum height?(g=10ms sq)

Answer 1

The stone is thrown upward from height, h = 85 m from the ground.

It reaches the ground in 5 s.

Let the initial velocity be ‘u’.

The displacement is ‘-85 m’ and acceleration is ‘-10 m/s2’ as they are downward so the negative sign comes.

Using,

S = ut + ½ at2

=> -85 = 5u – ½ × 10 × 52

=> u = 8 m/s

At the greatest height above the ground, the stone comes to momentary rest. That means its velocity becomes zero.

Using,

v2 = u2 + 2as

=> 0 = 82 – 2 × 10 × s

=> s = 3.2 m

Thus, the maximum height from the ground is = 3.2 + 85 = 88.2 m

Velocity with which it reaches the ground is,

v = u + at

=> v = 8 – 10 × 5

=> v = -42 m/s [downward]