Question

The drawing shows a collision between two pucks on an air-hockey table. Puck A has a mass of 0.0290 kg and is moving along the x axis with a velocity of +6.85 m/s. It makes a collision with puck B, which has a mass of 0.0580 kg and is initially at rest. The collision is not head-on. After the collision, the two pucks fly apart with the angles shown in the drawing. Find the speed of (a) puck A and (b) puck B. A goes up toward Q1 with 65 deg, B goes down towards Q4 with 37 deg

I've seen similar questions posted, I'll copy/paste my confusion below - note the numbers are different as it's from another posting:

Law of conservation of energy along x axis is ma v = ma v1 cos65 + mb v2 cos37 3.5kg(5.5 m/s) = (3.5kg) v1(0.4226) + (6kg) v2 (0.7986) 19.25 = 1.47 v1 + 4.79 v2 ----1

Law of conservation of energy along y axis is 0 = ma v1 sin 65 - mb v2 sin 37

Why is the law of conservation different along x and y axis - why is it ma+mb along x and ma-mb along y?

Answer 1