Question

Lorry of mass 4000 kg is travelling at a speed of 4.0 m/ s.

A car has a mass of 1000 kg. The kinetic energy of the car is equal to the kinetic energy of the lorry.
What is the speed of the car?

Answer 1

speed of the car = 8 m/sec

Step-by-step explanation:

For Lorry

Mass of the lorry m = 4000 kg

Speed of the lorry v= 4 m/sec

Kinetic energy of the lorry =
`(1)/(2) mv^(2)` =
`(1)/(2) 4000\cdot4^(2)` =32000 J

It is given that Kinetic energy of car = Kinetic energy of lorry

Hence, Kinetic Energy of car = 32000 J

For car

Mass of the car = 1000 kg

Suppose the speed of the car =
`v_c\ m/sec`

Kinetic energy of the car =
`(1)/(2) mv_c^(2)` =32000 J

`(1)/(2)1000\cdot v_c^(2)` =32000

`v_c^(2) =64\\v_c=8`m/sec

Hence speed of the car = 8 m/sec