A force of 16 N to the west is applied to each object below. Which object will undergo the greatest change in momentum?
A A 20 kg object that is moving east at 5 m/s
B A 20 kg object that is moving east at 10 m/s
C A 15 kg object that is moving east at 5 m/s
D A5 kg object that is moving east at 10 m/s

We must assume that the force is applied for equal amounts of time for all cases, since it doesn’t state otherwise. Therefore, the IMPULSE (or change in momentum) is EQUAL for all cases, no matter the specific masses or velocities! This would’ve been different if it asked us about the final momentum, but it’s not.

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A stone is thrown vertically upward with a speed of 17.0 m/s. How fast is it moving when it reaches a height of 11.0 m? How long is required to reach this height?

Let’s review the 4 basic kinematic equations of motion for constant acceleration (this is a lesson – suggest you commit these to memory):

s = ut + ½ at^2 …. (1)

v^2 = u^2 + 2as …. (2)

v = u + at …. (3)

s = (u + v)t/2 …. (4)

where s is distance, u is initial velocity, v is final velocity, a is acceleration and t is time.

In this case, we know u = 17.0m/s, a = -g = -9.81m/s^2, s = 11.0m and we want to know v and t, so from equation (2):

v^2 = u^2 + 2as

v^2 = 17.0^2 -2(9.81)(11.0)

v = √73.18 = 8.55m/s

now from equation (3):

v = u + at

8.55 = 17.0 – 9.81t

t = (8.55 – 17.0)/(-9.81) = 0.86s