Question

A truck drives to a rock quarry at a speed of 20 m/s. The truck takes on a load of rocks, which doubles its mass, and leaves at the same speed of 20 m/s. Quantitatively compare the kinetic energy of the truck as it left the quarry with its kinetic energy on the way to the quarry. Explain your answer.

Answer 1

Given that,

A truck drives to a rock quarry at a speed of 20 m/s. The truck takes on a load of rocks, which doubles its mass, and leaves at the same speed of 20 m/s.

To find,

Comparison of the kinetic energy of the truck as it left the quarry with its kinetic energy on the way to the quarry.

Solution,

Kinetic energy of an object is given by:

$K=\dfrac{1}{2}mv^2$

m is the mass of the truck

$K=\dfrac{1}{2}m\times (20)^2\\\\K=200m\ J$

If mass is doubled and speed is same i.e. 20 m/s, neew kinetic energy is given by :

$K=\dfrac{1}{2}\times (2m)\times 20^2\\\\K=400m\ J$

It can be seen that when mass of truck is doubled, its kinetic energy gets doubled.