Two carts with masses 10.0kg and 2.5 kg move in opposite directions on a frictionless horizontal track with speeds of 6.0m/s and 3.0 m/a respectively. The carts stick together after colliding head on. Find the final speed. Please help!!

When you jump from an elevated position you usually bend your knees upon reaching the ground. by doing this, you make the time of the impact about 10 times as great as for a stiff-legged landing. in this way the average force your body experiences is a) less than 1/10 as great. b) more than 1/10 as great. c) about 1/10 as great.d) about 10 times as great.