A bullet traveling at 250 meters per second is brought to rest by an impulse of 5.00 newton-seconds. What is the mass of the bullet?
The change of momentum of an object is equal to the impulse exerted on it.
Impulse is measured in units of newton-seconds
The change in the velocity is final minus initial, so
The negative number just means that the momentum has decreased, not increased, but we can ignore it in calculating the mass of the bullet. If we don't ignore it we end up with a negative mass, which doesn't make sense in this case.
Rearranging to make