An object falls freely from a height of 25m onto the roof a building 5m high. Calculate the velocity with which the object strikes the roof (g=10ms−²)?

A. 17.3ms−²
B. 20ms−²
C. 24.5ms−²
D. 125ms−²
E. 200ms−²

Correct Answer:

Option B = 20ms−²

Explanation

v²=u²+2as = 0+2×(25−5)

v²=0+20×20=400;

v = √400

=20ms−²