A 2.7-kg cart is rolling across a frictionless, horizontal track toward a 1.1-kg

Question

A 2.7-kg cart is rolling across a frictionless, horizontal track toward a 1.1-kg cart that is held initially at rest. The carts are loaded with strong magnets that cause them to attract one another. Thus, the speed of each cart increases. At a certain instant before the carts collide, the first cart's velocity is +4.3 m/s, and the second cart's velocity is 1.9 m/s. (Indicate the direction with the sign of your answer.) (a) What is the total momentum of the system of the two carts at this instant? kg · m/s (b) What was the velocity of the first cart when the second cart was still at rest? m/s

Explanation / Answer

a) Total momentum, P = m1v1 + m2v2

= 2.7*4.3 + 1.1*(-1.9)

= 9.52 kg m/s

b) Before they collided, the first cart had all the momentum, ie. its momentum was P.

P = m1v1

v1 = P/m1

= 9.52/2.7

= 3.526 m/s

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