2 An ice skater of mass 40 kg is moving in a straight line with speed \(4 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) when she collides with a skater of mass 60 kg moving in the opposite direction along the same straight line with speed \(3 \mathrm {~m} \mathrm {~s} ^ { - 1 }\). After the collision the skaters move together with a common speed in the same straight line. Calculate their common speed, and state their direction of motion.