Question

A 1 kg mass falls from a height of 10 m into a sand box. What is the speed of the mass just before hitting the sand box? If it travels a distance of 2 cm into the sand box before coming to rest, what is the average retarding force?

• A. $12m/s$ and $3600N$
• B. $14m/s$ by $4900N$
• C. $16m/s$ by $6400N$
• D. $18m/s$ by $8100N$

Answer 1

The correct option is B $14m/s$ by $4900N$

Potential energy of ball will convert to KE

SO, $mgh=\frac{m{v}^2}{2}\Rightarrow v=\sqrt{2gh}=\sqrt{2\times 9.8\times 10}=14m/s$

When object will pass through sand it will loose its KE to overcome the resisting force by sand.

Now $Fs=\frac{m{v}^2}{2}=98\Rightarrow F=\frac{98}{0.02}=4900N$