# Principles of Technology

## Year End Review: Mechanical Systems

### Mechanical Force (1:1)

1. What is a force?

2. What are the SI and English units of force?

3. What happens when forces are unbalanced?

4. A torque wrench has a lever arm of 30 cm. A force of 450 newtons is applied at the end of the wrench. Calculate the torque.

5. A torque wrench has a lever arm of 18 inches. A force of 85 pounds is applied at the end of the wrench. Calculate the torque.

6. A torque of 1750 N·M is produced by a wrench with a lever arm of 75 cm. How much force is being applied?

### Mechanical Work (2:1)

7. Barbara lifts a 180 lb. barbell to a height of 7.25 feet. How much work does she do?

8. While showing off for the guys, she holds the 180 lbs. over her head for 11.37 minutes. If you ignore the loss due to inertia, how much work does she do while maintaining the barbell in the raised position?

9. How many radians are in a full circle?

10. A winch with a crank handle one foot long applies a torque of 35 lb·ft. How much work is done to turn the winch through 15 revolutions?

11. A block and tackle is used to lift a load weighing 600 pounds. Robin lifts the load a distance of 1.25 feet by pulling on the rope with a force of 200 pounds over a distance of 4 feet. Calculate the following:

11a. input work

11b. output work

11c. efficiency of the block and tackle

12. If a winch has a lever arm of 1.25 feet and requires 40 pounds to turn the crank, how much work is done to turn the winch through 15 revolutions?

### Mechanical Rate (3:1)

13. What is the velocity of an object which travels 1500 meters northeast in 3.25 seconds?

14. What is the angular speed (in rev/min) of an fan which makes 540 revolutions in 40 seconds?

15. A 13.4 kilogram spitwad leaves Malone's hand and moves at a constant speed of 350 meters per second in the direction of Yura's head. It is in the air for 1.3 seconds before impact. How far does it travel?

16. Amber is fast asleep when the bell goes off. In her haste to reach her sweetie who is waiting in the lunch room, she accelerates to a speed of 80 miles per hour in 4.5 seconds. What is her rate of acceleration?

17. Derek is spinning on one foot. Assuming he doesn't get dizzy and fall down, what is his angular speed (in rads per second) if he completes 250 revolutions in 20 minutes?

18. An electric drill motor has an angular acceleration of 15 rev/sec2. It accelerates from a low speed of 275 rev/min to its highest speed in 4.7 seconds. Calculate the angular speed (in rev/min) of the drill at its highest setting.

### Mechanical Resistance

19. Dave is trying his best to push his little rubber boat through the water. Being the brute that he is, Dave is capable of exerting a force of 2200 N on the boat, and is maintaining a rate of 5.5 m/sec. Find the drag resistance on the U.S.S. Fluffnsuch.

20. A steel sled weighs 275 pounds and is sliding along a steel floor. Calculate the frictional force if the coefficient of kinetic friction (µk) = 0.09.