CHAPTER 5

1. (P.147 Prob.28) A 500 kg piano is being lowered into position by a crane while two people steady it with ropes pulling to the sides. Bob's rope pulls to the left, 15° below horizontal, with 500 N of tension. Ellen's rope pulls toward the right, 25° below horizontal.
   a. What tension must Ellen maintain in her rope to keep the piano descending at a steady speed?
   b. What is the tension in the main cable supporting the piano?
2. (P.148 Prob.36) Compressed air is used to fire a 50 g ball vertically upward from a 1.0-m-tall tube. The air exerts an upward force of 2.0 N on the ball as long as it is in the tube. How high does the ball go above the top of the tube?
3. (P.148 Prob.44) Johnny jumps off a swing, lands sitting down on a grassy 20° slope, and slides 3.5 m down the slope before stopping. The coefficient of kinetic friction between grass and the seat of Johnny's pants is 0.5.What was his initial speed on the grass?
4. (P.148 Prob.48) A horizontal rope pulls a 10-kg wood sled across frictionless snow. A 5.0-kg wood box rides on the sled. What is the largest tension force for which the box doesn't slip?
5. (P.150 Prob.71) (Challenge problem) You've enter a "slow ski race" where the winner is the skier who takes the longest time to go down a 15° slope without ever stopping. You need to choose the best wax to apply to your skis. Red wax has a coefficient of kinetic friction 0.25, yellow is 0.20, green is 0.15, and blue is 0.10. Having just finished taking physics, you realize that a wax to slippery will cause you to accelerate down the slope and lose the race. But a wax that's too sticky will cause you to stop and be disqualified. You know that a strong head wind will apply a 50N horizontal force against you as you ski, and you know that your mass is 75 kg. Which wax do you choose?