How much work need to be done to completely stop a car of 100 KG running at 50 m/s

Question

How much work need to be done to completely stop a car of 100 KG running at 50 m/s. 

Answer 1

You need to bring its kinetic energy down to zero, so the required work must equal the kinetic energy, but with a negative sign, since the applied force must oppose the direction of motion.

 

W = -mv²/2

 

m = 100 kg

v = 50 m/s

 

Just plug in the numbers and get the work in joules.