Question

A cement block accidentally falls from rest from the ledge of a 15.0m high building. When the block is 14.0m above the ground, a man who is 1.71m tall looks up and notices that the block is directly above him. How much time does he have to move out of the way?

Answer 1

Given that,

For free falling body, acceleration is equal to acceleration due to gravity.

a = g = 9.81 m/s²

Distance to be covered, s = 15 - 1.71

s = 13.29 m

At top initial velocity, Vi = 0

Since,

s = Vi *t + 1/2 at²

13.29 = 0 + 0.5 * 9.81 * t²

t = 1.646 s

The man have 1.65 seconds to move out of the way.