A car of mass 10 kg moves eastward at 30 m/s while a second car of mass 30 kg moves at 10 m/s westward. The magnitude of the linear momentum and the kinetic energy of the system are
A) 0 kg.m/s and 3.0 kJ.
B) 600 kg.m/s and 3.0 kJ.
C) 300 kg.m/s and 4.5 kJ.
D) 600 kg.m/s and 6.0 kJ.
E) 0 kg.m/s and 6.0 kJ.

Question

Quizplus · Accepted Answer

The total linear momentum of the system is 0 because the momentum of one car (10 kg * 30 m/s = 300 kg.m/s eastward) is equal and opposite to the momentum of the other car (30 kg * 10 m/s = 300 kg.m/s westward), canceling each other out. The total kinetic energy is the sum of the kinetic energies of both cars: $ \frac{1}{2} \cdot 10 \cdot 30^2 + \frac{1}{2} \cdot 30 \cdot 10^2 = 4500 + 1500 = 6000 $ Joules or 6.0 kJ, since kinetic energy is a scalar quantity and does not cancel out.

A Car of Mass 10 Kg Moves Eastward at 30