Practice Problems for Work, MA and Efficiency

Name: ______Date: ______Flynt - ___ Period ___th Grade Science

1. Speed measurements are given in units of A. distance/time B. time2/distance C. distance/time2 D. time/distance

2. A rider finished a 120-km bicycle trip in three hours. The average speed of the rider is… PSYW! a. 0.025 km/hr b. 360 km/hr c. 3.6 m/s d. 40 km/hr e. 4 m/s2

3. A car traveling at 25 m/s speeds up to 40 m/s over a period of 15 seconds. The average acceleration of the car is… PSYW! a. 1 m/s2 b. -1 m/s2 c. 15 km/s2 d. 15 m/s2

4. Which statement below best describes how to calculate acceleration? a. The change in distance divided by the change in time. b. The change in displacement divided by the change in time. c. The change in speed divided by the change in time. d. The change in velocity divided by the change in time.

5. The standard SI unit of measurement for force is a. The meter (m). b. The Newton (N). c. The gram (g). d. Pounds per square inch (psi).

6. An object CANNOT be accelerating if it has a constant speed. a. True b. False

7. According to Newton’s first law, if you throw a baseball in outer space where there is almost no gravity and no air (no opposing unbalanced forces) what should happen? a. The baseball would continue to fly in the same direction with a constant speed. b. The baseball would continue to fly with a constant speed, but its direction would change. c. The baseball would continue in the same direction, but its speed would decrease and it would eventually stop, just like here on Earth. d. The baseball would continue in the same direction, but its speed would increase. 8. List the four phases of matter in order from lowest kinetic energy to highest kinetic energy. a. Solid, Liquid, Gas, Plasma b. Plasma, Solid, Liquid, Gas c. Plasma, Gas, Liquid, Solid d. Gas, Plasma, Liquid, Solid

9. A roller coaster is rapidly picking up speed as it rolls down a big hill. At the very top, just as it starts down the slope, it is moving forward at 3 m/s. When it reaches the bottom 5 seconds later, its speed is 23 m/s. What is the coaster’s average acceleration from the top to the bottom of the hill? PSYW! a. 20 m/s b. 4 m/s/s c. -4 m/s/s d. 0.25 m/s/s

10. An airplane flies 80 km in 10 minutes and then flies 100 km in 20 minutes. The average speed of the airplane in kilometers per hour is… PSYW! a. 60 km/hr b. 360 km/hr c. 8 km/h d. None of the above

11. Suppose you are an astronaut who is currently doing work outside the space station, and your jet pack runs out of fuel. How can you use your empty jet pack to get you back to the station? a. Wave your arms and try to swim through space towards the shuttle. b. Throw your jet pack in the opposite direction of your space shuttle - your body will then move towards the shuttle. c. Yell for help!

12. The rate at which velocity changes is called A. instantaneous speed. B. direction. C. acceleration. D. motion.

13. On a graph showing position versus time, a horizontal line represents an object that is A. moving at a constant speed. B. increasing its speed. C. decreasing its speed. D. not moving at all.

14. The moon accelerates as it revolves around the Earth because it is a. in the vacuum in space. b. continuously changing direction. c. a very large sphere.

15. Which are complete descriptions of the momentum of an object? Circle all that apply. a. 2.0 kg/s d. 4.2 m/s, east b. 7.2 kg•m/s, right e. 1.9 kg•m/s, west c. 6.1 kg•m/s2, down f. 2.3 kg•m/s 16. Calculate the momentum value of a 2-kg brick moving forwards and to the right through the air at 12 m/s.

24 kgm/s right

17. Calculate the momentum value of a 3.5-kg wagon moving East along the sidewalk at 1.2 m/s.

4.2 kgm/s East

18. With what velocity must a 0.53-kg softball be moving to equal the momentum of a 0.31- kg baseball moving at 21 m/s?

12.3 m/s = velocity of the softball

19. How much work is done on a 75 N bowling ball when you carry it horizontally across a 10m wide room?

750 Nm = Work

20. How much work is done when a force of 1N moves a book 2m?

2 Nm = Work

21. What is the efficiency of a machine that requires 120J of input energy to do 35 J of useful work? 29% = % efficiency

22. If a steam engine does 500 J of useful work, how much work is needed to be put in if the efficiency rating of 18%?

2778 Joules = Work Input

23. What is the efficiency of a cyclist who expends 900J of work to his bike for it to produce 76 J of useful work?

8.4% = % efficiency