試題詳解

3. A block of mass 5 kg moving on a frictionless surface with a speed of 3 m/s collides with another block of mass 7 kg at rest. After the collision the two blocks stick together. What is the speed of the combined object?
(A) 1.25 m/s,
(B) 1.5 m/s,
(C)1 m/s,
(D) 0.5 m/s,
(E) 2.0 m/s.