- #1

- 97

- 0

## Homework Statement

1)A ball of mass 1.71 kg is dropped from a height y1 = 1.38 m and then bounces back up to a height of y2 = 0.88 m. How much mechanical energy is lost in the bounce? The effect of air resistance has been experimentally found to be negligible in this case, and you can ignore it.

What I did was I used the energy before = energy after. And I got 6.161J, however it seems that is wrong....

2)A car of mass 917 kg is traveling on a horizontal segment of a freeway with a speed of 58.8 mph. Suddenly, the driver has to hit the brakes hard to try to avoid an accident up ahead. The car does not have an ABS (antilock braking system), and the wheels lock, causing the car to slide some distance before it is brought to a stop by the friction force between the car's tires and the road surface. The coefficient of kinetic friction is 0.301. How much mechanical energy is lost to heat in this process?

Im not sure even how to start up this problem, Ive never done anything with heat :(

3)During an ice-skating extravaganza, Robin Hood on Ice, a 51.0-kg archer is standing still on ice skates. Assume that the friction between the ice skates and the ice is negligible. The archer shoots a 0.105-kg arrow horizontally at a speed of 99.4 m/s. At what speed does the archer recoil?

What I did was that there should be no change in momentum, but every time I solve it the computer says I have the wrong answer?? isnt it 0 = 51*v - .105*99.4 so v = .204 m/s?

4)A bungee jumper with mass 58.5 kg reaches a speed of 14.2 m/s moving straight down when the elastic cord tied to her feet starts pulling her back up. After 0.0250 s, the jumper is heading back up at a speed of 11.4 m/s. What is the average force that the bungee cord exerts on the jumper? and what is the average number g's experienced?

for the first part of that question I caculated the change in momentum which is impulse and I divided that by time and shouldnt that come out to the average force? I got 6552N, but apparently that is wrong, and how do you caculate the g's experienced?

I hate my teacher, and I AM TRYING TO LEARN, so please just dont give me the answer.