A 1 kg billiard ball collides head on with a 0.1 kg marble that sits at rest on the table. The marble moves at 3 m/s in the same direction the billiard ball was originally moving. The billiard ball continues after the collision at 0.3 m/s. What was the initial speed of the billiard ball?

Let v be the billiard ball's initial speed. The total momentum of the ball-marble system is conserved between the times before and after their collision, so that

(1 kg) v + (0.1 kg) (0 m/s) = (1 kg) (0.3 m/s) + (0.1 kg) (3 m/s)

Solve for v :

v + 0 = 0.3 m/s + 0.3 m/s

v = 0.6 m/s

the answer is kevlar

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west