There are 15 gymnasts in the US national team, with an average weight of 49kg. One more joins lowering the average by 0.5kg. How much does she weigh?
A ball weighing 10 grams hits a hard surface vertically with a speed of 5 meters/second and rebounds with the same speed. The ball remains in contact with the ground for 0.01 seconds. What is the average force exerted by the surface on the ball?