A 5 kg object moving with a speed of 6.6 m/s collides with an 18 kg object moving with a velocity of 8.4 m/s in a direction 19 degrees from the initial direction of the motion of the 5 kg object. What is the speed of the two objects after collision if they remain stuck together? Answer in m/s What is the change in direction experienced by the lighter of the two object? Answer in units of degrees.

Answer 1

Find initial momentum for the smaller object, via p1 = mv. Think of this momentum as being in the x-direction. Now break up the other objects momentum into its x and y components, p2x = mvcos(theta) and p2y = mvsin(theta). Final momentum in x-direction = p1+p2x and final momentum in y-direction = p2y. Use these components to find the momentum in the actual direction of the motion. Divide this momentum by the combined mass of the objects in order to find v. In order to find the change in direction, take the inverse tan of (p2y)/(p1+p2x). This is for the AP Physics students of decades to come.