Question

A spinning wheel is brought in contact with an identical wheel spinning at identical speed. The wheels slow down under the action of friction. Which of the following energies of the first wheel decreases?
(a) Kinetic
(b) Total
(c) Mechanical
(d) Internal

Answer 1

Kinetic and mechanical energies  decreases on slowdown of a wheel.

Explanation:

As we know that the kinetic energy is a function of mass and velocity and given by  

$KE = \frac{1}{2}mv^{2}$

Where, $m = \textrm{the mass of body}$

           $V = \textrm{the velocity of the body}$  

When velocity of body decreases then kinetic energy also decreases and mechanical energy is a summation of potential and kinetic energies.

If kinetic energy decreases then mechanical energy also decreases and kinetic energy is proportional to the temperature and If the wheel gets slowdowns due to friction, the mechanical energy is converted into heat energy and it leads to increase the internal energy.

So the correct answer is kinetic and mechanical energies.