Car X is travelling at half the speed of car Y. Car X has twice the mass of car Y.

Question 1

Car X is travelling at half the speed of car Y. Car X has twice the mass of car Y.

Which statement is correct?

A Car X has half the kinetic energy of car Y.

B Car X has one quarter of the kinetic energy of car Y.

C Car X has twice the kinetic energy of car Y.

D The two cars have the same kinetic energy.

Reference: Past Exam Paper – June 2004 Paper 1 Q17

Solution 1:

Answer: A.

Let the speed of car X = v.                 Speed of car Y = 2v

Let the mass of car X = 2m.               Mass of car Y = m

Kinetic energy = ½ mv²

KE of car X = ½ (2m) v² = mv²

KE of car Y = ½ (m) (2v)² = 2 mv²