Question

An object of mass 5kg travels in the positive direction with a speed of 1ms. The object collides with a second object that exerts an average net force over an interval of time such that the 5kg object comes to rest. Which of the following best predicts the change in momentum for the 5kg object?
A. The change in momentum is in the negative direction.
B. The change in momentum is in the positive direction.
C. The change in momentum is zero.
D. The direction of the change in momentum cannot be determined without knowing the value of the average force and time in which the force is exerted.

Answer 1

Answer: C. The change in momentum is zero.

Explanation: When an object is in movement, to change its direction or speed  we have to applied a force for determine amount of time. This change is called Change in Momentum or Impulse.

Change in momentum is a derivation of Newton's Second Law and can written as

                                            $F.t=m.\Delta v$

So, for the case discussed, object of mass 5kg already has momentum because it is already in motion. When another object collides with, applying a force for an interval of time, there is a change in momentum for the first object. Since the object stopped, it means velocity is 0, so as it is described in the formula, change in momentum is also 0.

In conclusion, "The change in momentum is zero" is the best prediction.