Question

A monkey sitting on a tree drops 10 g seed of rose-apple on a crocodile at rest below the tree. If the seed falls in the mouth of the crocodile in 2 s time and becomes stationary then the momentum gained by the crocodile (in addition to the seed) is ............ kgm/s. (g = 9.8 m/s²)
(A) 0.196
(B) -0.196
(C) 19.6
(D) -19.6

Answer 1

Answer:

(A) 0.196

Explanation:

Given,

mass of the seed= 10 g

time taken by seed to reach crocodile mouth= 2 s

acceleration due to gravity = g = 9.8 m/s²

so, the distance traveled by seed to reach crocodile's mouth ,

$h=\dfrac{1}{2}\times g\times t^{2}\\\\=\dfrac{1}{2}\times 9.8\times 2^{2}\\\\=19.6\ m$

At the top of the tree the seed will have has only potential energy while just before touching the mouth of crocodile it has only kinetic energy because according to conservation of energy the potential energy will get converted into kinetic energy.

$Hence,\ m.g.h=\frac{1}{2}\times m\times v^{2}\\\\=>\ v\ =\ \sqrt{2.g.h} \\\\=>\ v\ \sqrt{2\times 9.8\times\ 19.6}\\\\ => v\ =\ 19.6\ m/s$

Hence, momentum gained by crocodile= m x v

                                                                  =10 gm x 19.6 m/s

                                                                   =0.196 kg.m/s

So, the momentum gain by the crocodile is 0.196 kg.m/s.