Question

1).What is the momentum of a 900 kg sports car traveling down the road at a speed of 33 m/s? kg·m/s

2).What average net force is needed to accelerate a 1270 kg car to a speed of 29 m/s in a time of 7 s? N

3).A soft rubber ball (m = 0.4 kg) is falling vertically at 7 m/s just before it hits the ground and stops. What is the magnitude of the impulse acting on the ball? N·s If the ball had bounced instead, would the impulse be less than, equal to, or greater than what you calculated? less than equal to greater than

4).A very hard rubber ball (m = 0.2 kg) is falling vertically at 4 m/s just before it bounces on the floor. The ball rebounds back at essentially the same speed. If the collision with the floor lasts 0.05 s, what is the average force exerted by the floor on the ball? N

5).A woman with a mass of 60 kg runs at a speed of 10 m/s and jumps onto a giant 30 kg skateboard initially at rest. What is the combined speed of the woman and the skateboard? m/s

Answer 1

1) momentum = P = mv = 900 x 33 = 29700 kg m/s

2) car to a speed of from 0 to 29 m/s in a time of 7  

we know that

v = u + at

29 = 0 + a(7)

a = 29/7 m/s2

we know that F = ma = 1270 x 29/7 = 5261.4 N

3) impulse = i = F.t = ( mV/t )t =  mV = 0.4 ( 7-0) = 2.8 N-s

If the ball had bounced instead, the impulse would be greater than what we calculated.

4) F = P/t = mV/t = 0.2 [4-(-4)]/0.05 = 32 N

5) Fexternal = 0

Pi = Pf

60 x 10 = (60+30) x v

v = 6.67 m/s