PHYS 121 Lecture 17: Relativity II
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All diagrams taken from "l17_relativity. pdf" on the course canvas website. Quiz: consider two identical carts with inertia 2. 0 kg, initially pushed together with a compressed spring between them as shown, the cart-plus-spring system is set in motion with speed 1. 0 m/s. Then, the spring energy is released, after which one of the objects is found to be motionless. Enter your answer in joules but don"t include the units. Calculate the initial kinetic energy: 2 * . 5 mv2. Kinetic energy must go equally into both carts, the change in kinetic energy of the first cart is 1, so the second must also be 1. The system is closed so energy es in the spring is converted into the kinetic energy of the objects. It will be given by es = kf - ki. To get kf, we need the final speed of the moving object. The system is isolated, so conservation of momentum gives 2mvi = mvf or 2vi = vf.