Example #1: Push-Away With Energy

Practice: Two blocks (3 kg and 4 kg) on a smooth floor are pressed against a light spring (force constant 800 N/m) between them. When the blocks are released, the 3 kg is launched with 10 m/s.

(a) What speed is the 4 kg launched with?

(b) How much was the spring compressed by before the blocks were released?

Blocks A and B are initially at rest on a horizontal frictionless surface with a spring of negligible mass compressed between them. Block A has mass 5.0 kg and block B has mass 20.0 kg. The spring is released and the blocks move off in opposite directions. After the blocks, have moved away from the spring.
A) the magnitude of the momentum of block A is the same as the magnitude of the momentum of block B
B) the magnitude of the momentum of block A is less than the magnitude of the momentum of block B
C) the magnitude of the momentum of block A is greater than the magnitude of the momentum of block B

Two blocks are at rest on a horizontal frictionless surface with a compressed spring of negligible mass between them. Block A has mass 2.00 kg and block B has mass 5.00 kg. The blocks are released from rest and move off in opposite directions, leaving the spring behind. If block B has speed 0.800 m/s after it leaves the spring, what is the speed of block A after it leaves the spring? (Block A is the less massive block.)
(a) 0.63 m/s
(b) 0.95 m/s
(c) 1.00 m/s
(d) 1.26 m/s
(e) 1.50 m/s
(f) 2.00 m/s
(g) none of the above answers

Boxes A and B are at rest on a horizontal frictionless surface with a compressed spring of negligible mass between them. Box a has mass 2.0 kg and box B has 4.0 kg. When the spring is released the two boxes move off in opposite direction and the spring is left behind. After the boxes have moved away from the spring,A) the magnitude of the momentum of A is less than the magnitude of the momentum of BB) the magnitude of the momentum of A is greater than the magnitude of the momentum of BC) the magnitude of the momentum of A is equals than the magnitude of the momentum of BD) the kinetic energy of A equals the kinetic energy of B