Question

A block of mass $2.0\text{kg}$ slides on a rough surface. At $t=0$, its speed is $2.0\text{m/s}$. It stops after covering a distance of $20\text{cm}$ because of the friction exerted by the surface on it. Find the work done by friction.

• A. $-8\text{J}$
• B. $-4\text{J}$
• C. $-5\text{J}$
• D. $-7\text{J}$

Answer 1

The correct option is B $-4\text{J}$

The kinetic energy of ball at t = 0 is
$k=\frac{1}{2}m{v}^2=\frac{1}{2}\times \left(2.0\text{kg}\right)\times (2.0\text{m/s}{)}^2=4\text{J}.$
when the block comes to rest,its kinetic energy becomes zero. This loss of energy takes place because friction does negative work on the block.
Thus, the work done by the friction is $(-4\text{J})$