A 12,600 kg railroad car travels alone on a level frictionlesstrack with a const

Question

A 12,600 kg railroad car travels alone on a level frictionlesstrack with a constant speed of 18 m/s. A 5350 kg load initally atrest, is dropped onto the car. (a)What will be the car's new speed?(b) Also calculate the KE lost, and explain where it went. I got part (b) wrong on my homework. I dont know how to do it.The instructor did not show us or tell us how to solve it. pleasehelp. A 12,600 kg railroad car travels alone on a level frictionlesstrack with a constant speed of 18 m/s. A 5350 kg load initally atrest, is dropped onto the car. (a)What will be the car's new speed?(b) Also calculate the KE lost, and explain where it went. I got part (b) wrong on my homework. I dont know how to do it.The instructor did not show us or tell us how to solve it. pleasehelp.

Explanation / Answer

    Given that the mass of rail road car is M = 12,600 kg     Initial velocity of car is u = 18 m/s     Mass of load is m = 5350 kg ------------------------------------------------ Apply conservation of momentum             Mu = ( M + m ) v                v = Mu / ( M + m)                   = 12.63 m/s    This is the new speed of car Kinetic energy lost is K = Ki - Kf                                         = (1/2)Mu2 - (1/2)(M+m)v2                                         = ----------- J

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