Two blocks with masses 2.0 kg and 3.0 kg are placed on a horizontal frictionless surface. A light spring is placed in a horizontal position between the blocks. The blocks are pushed together, compressing the spring, and then released from rest. After contact with the spring ends, the 3.0-kg mass has a speed of 2.0 m/s. How much potential energy was stored in the spring when the blocks were released?
A) 15 J
B) 3.0 J
C) 6.0 J
D) 12 J
E) 9.0 J

Question

Quizplus · Accepted Answer

Explanation:The total momentum of the system is zero before and after the release. Therefore, the 2.0-kg mass must have a speed of 3.0 m/s after the release. The kinetic energy of the 3.0-kg mass is:$$KE_3 = (1/2)mv^2 = (1/2)(3.0 kg)(2.0 m/s)^2 = 6.0 J$$The potential energy stored in the spring is equal to the kinetic energy of the 3.0-kg mass:$$PE = KE_3 = 6.0 J$$

Two Blocks with Masses 2