# Need help on a tough ?

two masses are initially moving as follows: m1= 10.0 kg with a v1i = (0 m/s, 10 m/s), and m2= 5.00 kg with a v2i= (10 m/s, 0 m/s) THey collide and stick together, forming a composite mass of 15.0 kg. Use the principle of momentum conservation to find the magnitude (vf) and the direction of motion of the combined masses after the collisio.

that is the ? and i dont know where to begin at all someone help me please

Physics Monkey
Homework Helper
You have two masses moving in a plane. The masses collide and stick together. The question asks you to determine the speed of the composite object after the collision and its direction of motion. The problem tells you to use conservation of momentum, so what does conservation of momentum say?

Momentum is conserved in any collision if the effect of any external forces present is negliable relative to the effect of the collision

find the final momentum in the x and y directions.they must be equal to the initial momentum.
final momentum in x direction = M* v(x) = m1*v1(x) + m2*v2(x)
final momentum in y direction = M* v(y) = m1*v1(y) + m2*v2(y)
u know M=m1+m2, m1,m2 and v1 and v2.
find v(x) and v(y).

jtbell
Mentor
Physics Monkey said:
what does conservation of momentum say?
jmill5504 said:
Momentum is conserved in any collision if the effect of any external forces present is negliable relative to the effect of the collision
That is a description of the conditions under which conservation of momentum applies. It is not a description of the actual principle of conservation of momentum.
Conservation of momentum means that the total momentum of the two objects before the collision equals the total momentum of the two objects after the collision.

By the way, on a completely different subject, it really helps people here a lot if you put something in your thread's subject line that indicates what your question is about. For example, you could have used "Conservation of momentum problem".