# Physics homework - need help

We were given a WebAssign for homework dealing with forces. I got most of the problems, but there were a few I didn't understand at all. If anyone could help me, it would be much appreciated.

1. The helicopter in the drawing is moving horizontally to the right at a constant velocity. The weight of the helicopter is W = 59500 N. The lift force L generated by the rotating blade makes an angle of 21.0° with respect to the vertical. What is the magnitude of the lift force? Determine the magnitude of the air resistance R that opposes the motion.

2. A 85 kg water skier is being pulled at a constant velocity. The horizontal pulling force is 370 N. Find the magnitude of the upward force exerted on the skier by the water.

3. When a 58 g tennis ball is served, it accelerates from rest to a constant speed of 48 m/s. The impact with the racket gives the ball a constant acceleration over a distance of 44 cm. What is the magnitude of the net force acting on the ball?

jamesrc