Question

If a planet moves around the star in circular orbit then which quantity does not change with time? (a) speed (b) momentum (c) velocity (d) none of these

Answer 1

I think its speed will not change with time as velocity will change cause its direction will change and momentum is product of mass and velocity and velocity is changing so I think its speed will not change with change in time.

Answer 2

Speed of the planet does not change with time if it is revolving around the star.

Explanation:

Speed of the planet does not change because, we know that, the speed is the scalar quantity whereas, the velocity and momentum are the vector quantity.

Momentum is the product of mass and velocity.

Vector quantities are those quantities which has magnitude as well as direction for their definition.

Whereas, scalar quantities are those quantities which has only magnitude for their definition. These quantities does not depend on direction for their definition.