initial/final kinetic energy / work

Question

The velocity of a car of mass 1200kg changes of 10 m/s to 60 m/s.

a. Calculate the initial kinetic energy (K.Ei) of the car.

b. Calculate the final kinetic energy (K.Ef) of the car.

c. Write down the equation for the work energy theorem and from that equation find the work done

Answer 1

(a) Initial kinetic energy: 1/2*m*v^2 = 1/2*(1200 kg)*(10 m/s)^2 = 60000 kg m^2/s^2

(b) Final kinetic energy: 1/2*m*v^2 = 1/2*(1200 kg)*(60 m/s)^2 = 2160000 kg m^2/s^2

(c) Work energy theorem: W net = delta K or W net = K final - K initial

This is the work energy theorem. The change in kinetic energy is the work done in the system. The car just can't change from 10 to 60 m/s by itself, work has to be done in order for the energy to be increased (i.e. by the car motor).

Thus:

W net = K final - K initial = 2160000 - 60000 = 2100000 Kg m^2/s^2