Question

a body of mass 4kg is dropped from a height of 20m. calculate the initial momentum and the final momentum just before it strikes the ground. (g=10m/s).

Answer 1

s = 20m

u = 0 m/s

m = 4 kg

g = 10 m/s²

Initial momentum = mu

= 4×0

= 0 kg m/s

v²-u² = 2as

v²-0² = 2×10×20

v² = 400

v = √400

v = 20 m/s

Final momentum = mv

= 4×20

= 80 kg m/s

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Answer 2

Answer:

The initial momentum and final momentum of the body are zero  and 80kg.m/s respectively.

Explanation:

Given a body of mass, $m=4kg$

Height from where the body is dropped, $h=20m$

Acceleration due to gravity for freely falling body, $g=10m/s^{2}$

As the body is dropped from certain height,

the initial velocity of the body, $u=0$

Momentum of a body is given by the mass times its velocity i.e., $p=mv$

Thus the initial momentum of the body is

$p=m\times u=4\times u=0$

To find the final velocity of body, consider the equation of motion, $v^2-u^2=2as$

$v^2-0=2\times 10\times 20=400$

$v=\sqrt{400} =20m/s$

Therefore, the final velocity is 20 m/s.

And thus the final momentum of the body is

$p=m\times v=4\times 20=80 kg.m/s$

Therefore, the initial momentum of the body is zero and final momentum before it strikes the ground is 80kg.m/s.