Question

A 1.0-kg block and a 2.0-kg block are pressed together on a horizontal frictionless surface with a compressed very light spring between them. (The blocks are not attached to the spring.) The blocks are then released and the spring uncompresses. Immediately after the blocks lose contact with the spring, which statement below is true?A. the magnitude of the momentum of the heavier block will be greater than the magnitude of the momentum of the lighter block.B. the lighter block will have more kinetic energy than the heavier block.C. both blocks will both have the same amount of kinetic energy.D. both blocks will have equal speeds.E. the heavier block will have more kinetic energy than the lighter block.

Answer 1

Answer:

statement B is true

Explanation:

since same force is applied by the compressed spring on both masses so their rate of change of momenta must be same and since the lighter block has lesser mass so it must have greater velocity to have an equal change in momentum as of heavier mass.

By relation: $KE=\frac{(mv)^{2} }{2m}$

$KE lighter=\frac{(mv)^{2} }{2(1)}$ , $KEheavier=\frac{(mv)^{2} }{2(2)}$

comparing momenta of above two equations we get

KElighter (2) = KEheavier (4)

KElighter = 2 KEheavier