Lesson 1 : Basic Terminology and Concepts

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9. A tired squirrel (mass of approximately 1 kg) does push-ups by applying a force to elevate its center-of-mass by 5 cm in order to do a mere 0.50 Joule of work. If the tired squirrel does all this work in 2 seconds, then determine its power.

0.25 Watts

0.75 Watts

1.00 Watts

None of the above

The tired squirrel does 0.50 Joule of work in 2.0 seconds. The power rating of this squirrel is found by

P = W / t = (0.50 J) / (2.0 s) = 0.25 Watts

Explanation

The tired squirrel does 0.50 Joule of work in 2.0 seconds. The power rating of this squirrel is found by

P = W / t = (0.50 J) / (2.0 s) = 0.25 Watts

10. When doing a chin-up, a physics student lifts her 42.0-kg body a distance of 0.25 meters in 2 seconds. What is the power delivered by the student's biceps?

51.5 Watts

75.0 Watts

25.0 Watts

None of the above.

To raise her body upward at a constant speed, the student must apply a force which is equal to her weight (m•g). The work done to lift her body is

W = F * d = (411.6 N) * (0.250 m)
W = 102.9 J

The power is the work/time ratio which is (102.9 J) / (2 seconds) = 51.5 Watts (rounded)

Explanation

To raise her body upward at a constant speed, the student must apply a force which is equal to her weight (m•g). The work done to lift her body is

W = F * d = (411.6 N) * (0.250 m)
W = 102.9 J

The power is the work/time ratio which is (102.9 J) / (2 seconds) = 51.5 Watts (rounded)

11. An escalator is used to move 20 passengers every minute from the first floor of a department store to the second. The second floor is located 5.20 meters above the first floor. The average passenger's mass is 54.9 kg. Determine the power requirement of the escalator in order to move this number of passengers in this amount of time.

1000 W

933 W

879 W

None of the above.

A good strategy would involve determining the work required to elevate one average passenger. Then multiply this value by 20 to determine the total work for elevating 20 passengers. Finally, the power can be determined by dividing this total work value by the time required to do the work. The solution goes as follows:

W1 passenger = F • d • cos(0 deg)
W1 passenger = (54.9 kg • 9.8 m/s2) • 5.20 m = 2798 J (rounded)

W20 passengers = 55954 J (rounded)

P = W20 passengers / time = (55954 J) / (60 s)

P = 933 W

Explanation

A good strategy would involve determining the work required to elevate one average passenger. Then multiply this value by 20 to determine the total work for elevating 20 passengers. Finally, the power can be determined by dividing this total work value by the time required to do the work. The solution goes as follows:

W1 passenger = F • d • cos(0 deg)
W1 passenger = (54.9 kg • 9.8 m/s2) • 5.20 m = 2798 J (rounded)

W20 passengers = 55954 J (rounded)

P = W20 passengers / time = (55954 J) / (60 s)

P = 933 W

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Lesson 1 : Basic Terminology and Concepts

1. __________ is the stored energy of position possessed by an object.

2.

What first name or nickname would you like us to use?

2. Two physics students, Will N. Andable and Ben Pumpiniron, are in the weightlifting room. Will lifts the 100-pound barbell over his head 10 times in one minute; Ben lifts the 100-pound barbell over his head 10 times in 10 seconds. Which student does the most work? ______________

3. The total amount of mechanical energy is merely the sum of the __________ and the kinetic energy.

4. The standard metric unit of Energy is the __________.

5. There are two forms of potential energy discussed in our course - gravitational potential energy and __________.

6. Mechanical energy can be either kinetic energy ( __________ ) or potential energy (stored energy of position).

7. __________ is the energy stored in elastic materials as the result of their stretching or compressing.

8. __________ is the energy stored in an object as the result of its vertical position or height. The energy is stored as the result of the gravitational attraction of the Earth for the object.

9. A tired squirrel (mass of approximately 1 kg) does push-ups by applying a force to elevate its center-of-mass by 5 cm in order to do a mere 0.50 Joule of work. If the tired squirrel does all this work in 2 seconds, then determine its power.

10. When doing a chin-up, a physics student lifts her 42.0-kg body a distance of 0.25 meters in 2 seconds. What is the power delivered by the student's biceps?

12. __________ is the energy that is possessed by an object due to its motion or due to its position.

13. An object that possesses mechanical energy is able to do __________.

14. The standard metric unit of power is the __________.

15. The expression for power is __________.

16. An object that has motion - whether it is vertical or horizontal motion - has __________ .

17. In terms of potential energy, the equilibrium position could be called the __________.

18. An object possesses gravitational potential energy if it is positioned at a height above (or below) the __________ height.

19. Two physics students, Will N. Andable and Ben Pumpiniron, are in the weightlifting room. Will lifts the 100-pound barbell over his head 10 times in one minute; Ben lifts the 100-pound barbell over his head 10 times in 10 seconds. Which student delivers the most power? ______________

20. There are three key ingredients to work - force, displacement, and __________.