total momentum of the system?

Question

A 5.0 kg ball is moving at 4.0 m/s to the right and a 10 kg ball is moving at -2.0 m/s to the left. The total momentum of the system is??

a) 0.0 to the right
b) 20 kg m/s to the left
c) -20 to the right
d) 40 to the left
e) 17 to the right

please help/explain thanks

Answer 1

a) 0. You wouldn't normally give a direction for a zero value.

Total momentum is just the sum of (mi)(vi) for each individual object, where mi is the mass of object i and vi is the velocity of object i. i refers to the indices of the objects, which can be assigned arbitrarily. If the 5.0 kg ball is object 1 (i = 1) and the 10 kg ball is object 2 (i = 2), total momentum is (m1)(v1) + (m2)(v2) = (5 kg)(4 m/s) + (10 kg)(-2 m/s) = (20 kg-m/s) + (-20 kg-m/s) = 0 kg-m/s.

Answer 2

THIS QUESTION IS ASKED INCORRECTLY. -2.0 m/s to the left is equivalent to +2.0 m/s to the right (because left and right are in opposite directions). Momentum is mass times velocity. So the CORRECT total momentum to the right is,

5.0*4.0+10.0*2.0=+40 kg m/s to the right

I KNOW MY PHYSICS, THAT IS DEFINITELY THE CORRECT ANSWER, BUT IT IS NOT GIVEN AS A CHOICE!

This is a badly written question! I suspect that when they say "-2.0 m/s to the left", what they REALLY meant to say was "+2.0 m/s to the left". In that case we would say a velocity of +2.0 m/s to the left is the same as -2.0 m/s to the right. The total momentum to the right is then,

5.0*4.0+10.0*(-2.0)=0

It's zero, so left or right makes no difference.

I say again, this is a terrible question, don't let it confuse you!

Answer 3

Total momentum of the system = (5)(4.0) + (10)(-2) = 0

Answer 4

because of the prolem right here is the ideas Use the Conservation of momentum 4.5(-2i+6j-5k)+5(i-2j-4k)=Momentum <=>-9i+27j-22.5k+5i-10j-20k=Momentum <=>-4i+17j-40 two.5k=Momentum --- it is the respond