At what speed does a 2000 kg compact car have the same kinetic energy as a 18000 kg truck going 21 km/hr?

v = 17.5 m/s = 63 km/h

Explanation:

The general expression for the kinetic energy of one moving object is as follows:

       

       where m = mass of the object, v= speed of the object.

In order to get the value of the kinetic energy of the truck in Joules, we need to convert km/hr to m/s first, as follows:

       

Now, replacing (2) and m = 18000 kg in (1), we get:

       

This value must be the same for the 2000 kg compact car, so we can write:

       

Solving for v, we get: