Question

A car has a kinetic energy of 1.9 × 10^3 joules. If the velocity of the car is decreased by half, what is its kinetic energy?

Answer 1

The initial kinetic energy of the car is

`E_1 = (1)/(2)mv_1^2 = 1.9 \cdot 10^3 J`

Then, the velocity of the car is decreased by half:
`v_2 = (v_1)/(2)`
so, the new kinetic energy is

`E_2 = (1)/(2)mv_2 ^2 = (1)/(2) m ( (v_1)/(2) )^2= (1)/(2)m (v_1^2)/(4)= (E_1)/(4)`
So, the new kinetic energy is 1/4 of the initial kinetic energy of the car. Numerically:

`E_2 = (1.9 \cdot 10^3 J)/(4)=475 J`