Which car has the greatest kinetic energy?

Question

Car B is traveling twice as fast as car A, but car A has twice the mass of car B. Which car has the greatest kinetic energy and by what factor is it greater?

Answer 1

Kinetic Energy is defined by 1/2 times the mass times the velocity squared.

 

KE = (1/2)mv²

 

 

Suppose Car A has

 

m = 1 kg

v = 2 m/s

 

 

Then Car B has

 

m = 1/2 kg

v = 4 m/s

 

 

Find the KE for both cars and compare their energies.

 

Car A

KE = (1/2)(1 kg)(2 m/s)²

     = 2 Joules

 

Car B

 

KE = (1/2)(1/2 kg)(4 m/s)²

     = 4 Joules

 

Car B has the greatest kinetic energy by a factor of 2 joules.