Question

A mass of 5kg is on top of a building of height 10m. Calculate its potential energy.
The mass then falls at a speed of 8 m/s in 4 sec, find its KE and momentum p. What is the Force and impulse the mass transfers to the ground?

Answer 1

Potential energy:

$$E=mgh=(5)(9.8)(10)=490\ J$$

$$KE=0.5mv^2=0.5(5)(8)^2=160\ J$$

 

$$P=mv=(5)(8)=40\frac{kgm}{s}$$

​ ​ The impulse the mass transfers to the ground:

$$I=P=40\frac{kgm}{s}$$

The force:

$$F=\frac{I}{t}=\frac{40}{4}=10\ N$$