A ball with a mass of 0.50 kilograms is moving at a speed of 1.8 meters/second along the positive x-axis. It collides with another ball of the same mass travelling at a speed of 2.0 meters/second toward the positive y-axis. Both balls then start moving together. What is the magnitude of the resultant momentum before collision?

Question

A. 1.3 kilogram meters/second
B. 1.5 kilogram meters/second
C. 1.8 kilogram meters/second
D. 2.1 kilogram meters/second

Answer 1

Try applying conservation of momentum.
The resultant momentum of both objects (taken together) will be conserved.

sqrt[(0.5*1.8)^2 + (0.5*2.0)^2] = 1.3454 kg m/s

They want you to keep just two significant figures, so use 1.3.