1) A 50 kg woman stands on a bathroom scale while riding in an elevator descending with decreasing speed (magnitude of acceleration is 2 m s-2). Draw a free body diagram for the woman. What is the reading on the scale?
If you get the free body diagram correct then this is an easy problem. Think about how you feel on an elevator, or better still go and ride the elevator. Does your answer make sense?
2) A fire hose has an opening whose radius is 10 cm. The hose discharges water at a velocity of 20 ms-1. How much force is required by the fireman to hold the nozzle stationary? A fire hose ejects a stream of water with a speed of 20 m s-1, as above. At what angle to the horizontal should the fire hose be directed if it is to remove the civil liberties of protesters 20 m from where the hose is being held?
i. There are two parts to this problem. In the first part you have to calculate the force required to hold the fire hose. To do this go back to the definition of force. Its not necessarily , because this assumes the mass is constant. Here its the opposite the velocity of the water is constant, and acceleration is zero, but the mass changes as more and more water is being ejected. Go back to the definition of force from the momentum section in the notes.
ii. The second part is simply a range equation plug and chug problem.
3) A 20 kg monkey has firm hold on a light rope that passes over a frictionless pulley and is attached to a 20 kg bunch of bananas. The monkey looks up, sees the bananas, and starts to climb the rope to get them.
As the monkey climbs do the bananas move up, down or remain at rest? Explain.
As the monkey climbs, does the distance between the monkey and the bananas increase, decrease, or remain the same? Explain.
The monkey releases her hold on the rope. What happens to the distance between the monkey and the bananas while she is falling?
Before reaching the ground, the monkey grabs the rope to stop her fall. What do the bananas do?
A FBD might help here. Have fun!