# A boy jumps from a wall 3m high. What is an estimate of the change in momentum of the boy when he lands without rebounding?

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A. 5 N/s

B. 50 N/s

C. 500 N/s

D. 5000 N/s

The answer is C, but why?

A. 5 N/s

B. 50 N/s

C. 500 N/s

D. 5000 N/s

The answer is C, but why?

##### 1 Answer

See explanation.

#### Explanation:

It is **not** possible to give the answer as an exact number if the boy's mass is not given.

The boy's end velocity can be calculated using the energy preservation law:

#E_k=E_p#

The equation comes from the fact that all boy's initial potential energy is transferred to kinetic energy.

#mgh=(mv^2)/2#

#v^2=2gh#

#v=sqrt(2gh)~~7,75#

So the change in momentum is:

where

Looking at the answers we find that if the mass is about

The second part (referring to answers