A train car rolls on a frictionless track at a constant speed of v_0. Inside the

Question

A train car rolls on a frictionless track at a constant speed of v_0. Inside the train car is a block held in place within the car such that it compresses a spring on one end of the car, as shown in the diagram to the right. The block is then released so that the spring launches it forward within the car as the car rolls. In which of the situations depicted below will the speed of the center of mass of this system (train + block + springs) be equal to v_0? The state of the block's motion within the car and whether there is kinetic friction between the block and the floor of the car is provided. a. A only b. A & B only c. A & C only d. A, B, & C e. none of these

Explanation / Answer

When left side spring release the block it will go to its right side spring and settle if there is no friction between the floor and the block. At constant velocity, the net force on the block must be zero. Only the spring exerts a horizontal force on the block so it must read zero and is shown in A whereas if there is a friction the block would stopped by floor and it continues in the same point as shown in C.

A and C are true if or if not friction is acting

Option C - A & C only

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