Question

A body, having kinetic energy k, moving on a rough horizontal surface, is stopped in a distance x. The force of friction exerted on the body is

• A. $\frac{k}{x}$
• B. $\frac{\sqrt{k}}{x}$
• C. $\frac{k}{\sqrt{x}}$
• D. $kx$

Answer 1

The correct option is A

$\frac{k}{x}$

Let f be the force of friction and m be the mass of the body.

The retardation a = f / m. If v is the initial speed of the body, then

$2ax=v^2$

or $max$ =$\frac{1}{2}m{v}^2=k$

But $ma=f$. Therefore $fx=k$ or $f=\frac{k}{x}$.