An open railroad car of mass 2402 kg is coasting with an initial speed of 19 m/s

Question

An open railroad car of mass 2402 kg is coasting with an initial speed of 19 m/s on a frictionless, horizontal track. It is raining, and water begins to accumulate in the car. After some time, it is found that the speed of the car is only 9 m/s. How much water (in kilograms) has accumulated in the car? 2668.8 kg Consider the collision between two hockey pucks in the figure below. They do not stick together. Their speeds before the collision are v_1 = 26 m/s and v_2 = 12 m/s. It is found that after the collision one of the pucks is moving along x with a speed of 5 m/s. What is the final velocity of the other puck? magnitude 213 m/s direction 63.13 degree counterclockwise from the +x- axis.

Explanation / Answer

Conserve momentum: initial p = final p
initial p = M*(28m/s*cos30) i + M*(12m/s - 28m/s*sin30) j
initial p = M*24.248m/s i - M*2m/s j
final p = M*(6m/s + Vcos) i + M*Vsin j
The i-components must be equal, as must the j-components:
24.248 m/s =5m/s + Vcos Vcos = 19.248 m/s #1
-2m/s = Vsin #2
Divide #2 by #1
Vsin / Vcos = tan = -2m/s / 19.248m/s
= -5.932º (that is, below the x-axis)
V = -2m/s / sin-5.932º

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