Question

if the mass of a moving object decreases from 100 grams to 25 grams, what happens to its momentum?

a. its reduced 1/4 of the original momentum
b. its reduced 1/2 of the original momentum
c. not affected by change in mass
d. becomes 4 times the orignal momentum

Answer 1

The correct answer is c. not affected by change in mass

The law of conservation of momentum states that, for an isolated object (=zero net external force acting on it), the momentum of the object is conserved.

As a result, if there are no external forces acting on the object in the problem, its momentum will not change even though its mass changes. In fact, the momentum is given by the product between mass and velocity:

$p=mv$

therefore, when the mass of the object decreases by a factor of 4, the velocity will increase by a factor of 4, keeping the momentum of the object constant.