An 18, 000 kg semi containing Lex Luthor in the process of stealing forty cakes is moving with a speed of 15 m/s . If Superman is to stop the van in 0.5 seconds, what force must he exert on the van?

540000 Newtons

Explanation:

F = m*a

Acceleration =

The van is originally travelling at 15m/s, if superman stops the car, then it ends with a velocity of 0m/s, and he does this in 0.5 seconds. Therefore the acceleration of superman stopping the van is   (Final velocity - initial velocity) / Time

Mass of van is 18,000 kg.

Force = 18,000 kg * -30m/s^2

Note that force is scalar, so it is always positive regardless of the sign of acceleration.

540000 N