Question

A car is moving with a speed of 15 km h^-1 and another identical car is moving with a speed of 30 km h^-1. Compare their kinetic energy.

Answer 1

Two identical cars mean, they have equal mass
K.E = 1/2 mv²
Let m be the mass of each car

Kinetic energy of car A = `1/2` m × `(15)^2` = `225/2` m 

                                                                 = 112.5 m J        
Kinetic energy of car B = 1/2 M (30)²
=450 M J

`(K.E. of A) /(K.E. of B)` = `(225 m )/(2 × 450 m )` = `1/4` = 1 : 4
K.E. of car B is 4 times K.E. of car A.