What would be the change in momentum if a ball of 20N was experiencing a force of 50N for 0.25 seconds?

Question

Because the unit for change of momentum is kg m/s, would I have to convert the N into kg before I did it ?

Answer 1

No just multiply the time with the diff in force and weight (50-20)x0.25 Because newton is actually kg m/s^2

Answer 2

Force = f = ma = m dv/dt = d(mv)/dt = dp/dt; where m is mass, a is acceleration (dv/dt), v is velocity, and p is momentum = mv. Thus change in momentum (over time) is caused by that force f. Therefore, f dt = dp and the change in momentum is simply the net force (f) times the time interval (dt).

So, the real question is, what's the net force? One answer questioned whether the weight of the ball (W = 20 N) would have any effect on change in momentum. I think not, the weight is a downward force, and, I presume, the "force" is a sideways force. Thus, the change in momentum (sideways) is just f dt = dp = 50 X .25 = 12.5 N-sec.

On the other hand (where there are four fingers and a thumb), if your 50 N nudge is upward against the weight, then f = (F - W) = 30 N and f dt = dp = 30 X .25 = 7.5 N-sec

And, as one astute answerer put it, you do not need to go into kg etc. because weight is a force and its force times delta time that gives the change of momentum in force-time units.

Answer 3

delta p = impulse = force * time

The weight of the ball doesn't matter (unless you are counting that as an additional force, which I don't think you should the way I read the problem)--it's the force on it that gives an impulse. If they did mean for you to count the weight as an additional force, they would need to give you some more information about the directions of the forces so you could properly combine them.