# Momentum and force

## Main Question or Discussion Point

let us say there is a mass m. A push is applied at one end for 2seconds. The velocity of the mass changes to v2. So the force applied is
m*v2/2. But momentum is m*v2.

My query is when momentum should be used or has to be used?

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quasar987
Homework Helper
Gold Member
I cannot imagine a more vague question. What exactly do you want to know?

P.S. You should have specified that the force applied to the block is a constant force.

lightgrav
Homework Helper
Momentum is a property of the object,
retained by it even after the Force quits.

Use momentum whenever you want to describe an object.

Use Force when you want to describe an interaction
that changes the motion of an object.

(scold: don't forget the unit "seconds"! Force = m * v2 / (2 )

Generally, a constant force applied to a particle (i assume the mass you are talking about is a mass point) during time is defined as the impulse of the force, more precisely $$S_{1,2}=\int_{t_{1},t_{2}}{Fdt}=mv_{2}-mv_{1}$$, where the velocities, the impulse and the force are all vector quantities. So, you can conclude that a force that acts on a particle in a time interval, results with a change of linear momentum. I think everything should be clear now :)