A block of mass m = 3.7 kg slides from left to right across a frictionless surface withra speed v; - 7.4 m/s. It collides in a perfectly elastic collision with a second block of
mass M that is at rest. After the collision, the 3.7-kg block reverses direction, and its new speed is vf 2.2 m/s. What is M?
8.9 kg
6.8 kg
5.2 kg
7.5 kg