A body is dropped from a height of 20 metres with zero initial momentum; calculate its
mass if it hits the ground with momentum 40 kg. m/s. (Assume the acceleration due to gravity 'g' = 10 m/s2)
Show answer & explanation
Correct answer: D
Explanation
The correct answer is Option 4 i.e. 2 kg.
Height h = 20 m, initial speed u = 0
g = 10 m/s2
Momentum at impact p=40 kg
First, find the impact speed using v2 = u2 + 2gh:
v = 2gh = 2×10×20 = 400 = 20m/s.
Momentum p = mv ⇒ m = p/v = 20/ 40 = 2kg.
m = 2 kg