Student Workbook
for
Physics
Quarter 2

(Work, Energy and Power)


Physics - Force Brush Up Handout 5-0 to practice before beginning energy


Physics - Work and Energy Handout 5-1

1. If friction is neglected for figure A, determine:
a) the value of F needed to cause an acceleration of 2.0 m/s2 to the right.

b) the work done by the force F as it moves 5.0-m to the right.

c) the work done by gravity as it moves 5.0-m to the right.

d) the work done by the normal force as it moves 5.0-m to the right.

f) the net work done on the box.

2. If the coefficient of friction for figure A is 0.22, determine:
a) the value of F needed to cause an acceleration of 2.0 m/s2 to the right.

b) the work done by the force F as it moves 5.0-m to the right.

c) the work done by gravity as it moves 5.0-m to the right.

d) the work done by the normal force as it moves 5.0-m to the right.

e) what type of friction is being considered and the work done by friction

as it moves 5.0-m to the right.

f) the net work done on the box.

3. If the coefficient of friction for figure B is 0.22, determine:
a) the value of F needed to cause an acceleration of 2.0 m/s2 to the right.

b) the work done by the force F as it moves 5.0-m to the right.

c) the work done by gravity as it moves 5.0-m to the right.

d) the work done by the normal force as it moves 5.0-m to the right.

e) what type of friction is being considered and the work done by friction

as it moves 5.0-m to the right.
f) the net work done on the box.

4. If the coefficient of friction for figure C is 0.22, determine:
a) the net work done on the box? The box moves 2.0m

b) the work done by gravity as it moves 2.0-m downhill.

c) the work done by the normal force as it moves 2.0-m downhill.

d) what type of friction is being considered and the work done by friction

as it moves 2.0-m downhill.

5. A crane lifts a (1100-kg) car vertically at a constant speed. If the car is raised a total height of 4.0-m determine:
a) the value of the force needed to lift the car. c) the work done by gravity.
b) the work done by this lifting force. d) the net work done on the car.

6. A crane lifts a (1100-kg) car vertically with an acceleration of 0.75 m/s2. If the car is raised a total height of 4.0-m during this acceleration determine:
a) the value of the force needed to lift the car. c) the work done by gravity.
b) the work done by this lifting force. d) the net work done on the car.

7. An electron has a mass of 9.11 x 10-31kg. A certain elephant weighs 6600-Lbs. If this elephant walked with a speed of 2.1 m/s would it be possible for the electron to have the same kinetic energy? Support your answer.
HINT: the speed of light is 6.706 x 108 mph and there are 1609 meters in a mile.

8. What is the airspeed of an unladen swallow? What do you mean; an African or European Swallow?
If the average mass of a European Swallow is 20.3-grams and that of the Aftican Swallow is 141.75-grams determine the speed of each when they have the same kinetic energy (1.228Joules).

9. Which has more potential energy: a 10-pound bowling ball that is 1-0 meter above the ground or a 2.7-gram ping pong ball that is 1000-m above the ground?

10. How much energy is stored in a pinball machine spring (constant = 750 N/m) that is compressed 3.0-cm?

11. Mrs Klein (59-kg) climbs a ladder to the top of the roof (3.8-m) in 18-seconds. Mr. Bruening (115-kg) completes the same task in 22-seconds and Mrs. Austin (55.5-kg) can do it in 15-seconds. Rank the teachers in order of the most powerful to the least.

12. A corvette can go from 0 – 60 mph in 4.3 seconds. If the mass of the car is 1443-kg how much work is required to complete this task (assuming it is on a horizontal road)? B) What is the power (in HP) of the corvette?

13. How much work is required to lift a 10-kg object above your head (approximately 1.3-m)?

14. An 1100-kg car accelerates from rest to 90-km/h over a distance of 25.0-m. How much work is done? B) What is the average force applied through this distance?

15. A fighter jet (mass = 6020kg) is launched from an aircraft carrier with the aid of its own engines and a catapult. The thrust of the engines is 23000N. In being launched from rest is moved through a distance of 87-m and has a kinetic energy of 4.5 x 107 J at lift off.
a) what is the acceleration of the jet? B) what is the work done by the engines? C) what is the work done by the catapult?


Physics - Work and Energy Handout 5-2

1. A stuntman stands atop of a high platform. At the top of the platform his potential energy is 15,000J. If he jumps from the platform (vo = 0), determine his potential and kinetic energies at the following locations: use the grid below to graph your answers

½ the way down
Etotal / PE / KE
¾ the way down
Etotal / PE / KE
all the way down
Etotal / PE / KE

2. For the situation described in problem 1, how fast is the 490 N man traveling when he reaches the ground assuming there was no loss of mechanical energy?

3. A 105-g hockey puck is sliding across the ice. A player exerts a constant horizontal force of 4.5N over a distance of 15-cm. How much work is done on the puck?

4. A 10-kg block is released from rest at the top of the incline shown in figure B. If the block has a mass of 10.0-kg determine the: Neglect friction

a) speed at the bottom of the incline.

b) acceleration of the block.

5. If friction is not neglected and the 10 kgblock is released from rest at the top of the incline shown in figure B determine:

a) work done by friction if the block is moving with a speed of 3.5 m/s when it reaches the bottom.

b) the value of the frictional force.

c) the work done by gravity as it slides down the hill

d) the net work done

e) the acceleration of the block

6. A car accelerates from 8.0 m/s to 12.0 m/s in 4.5 seconds. What is the work done during this acceleration? You may assume that the car travels horizontally. The car has a mass of 1050-kg

7. A shopper in a supermarket pushes a cart with a force of 35 N directed at an angle 25° downward with the horizontal. What is the work done by this force as the cart moves 20.0m down the aisle?

b) If the coefficient of kinetic friction between the wheels and the floor is 0.15, what is the work done by the frictional force? The cart has a mass of 4.5-kg

8. A 2.0-g bullet leaves the barrel of a gun with a speed of 300m/s. What is the work done in accelerating the bullet ? b) Find the average force exerted on the bullet by the expanding gases as the bullet moves the length of the 50.0cm long barrel.

9. A weight lifter lifts a 350-N set of weights from the ground to a vertical distance of 2.00m. How much work does the weight lifter do in lifting the weight? How much work does gravity do during this process?

10. A 1300-kg elevator is lifted upward by a cable. If the elevator accelerates upward at a rate of 0.65 m/s2 determine:

a) the magnitude of the lifting force.

b) the work done by this force as it moves 5.0m


Physics - Work and Energy Handout 5-3

Work (W) à work is the (scalar) product of the parallel component of a force and the displacement through which that force is applied.
Pay attention to:
1. Which force the problem is referring to.

2. The direction of the force…is it parallel to the distance?
3. The direction of the force…is it positive (with the direction) or negative (opposite the direction)?

1.  A 10-kg box is pushed to the right via a force, F, as shown. There is friction between the box and the floor; the kinetic coefficient is 0.37. If the box moves 5.0-m at a constant speed determine:

a) the magnitude of the force, F. d) the work done by gravity
b) the work done by the applied force, F. e) the work done by the net force.
c) the work done by friction. F) the work done by the normal force.

2.  A 12-kg box is pushed UP an incline via the force, F, as shown.
the value of the force, F, is 100-N and the box accelerates uphill at 1.5 m/s2

Determine the work done by each of the following if the box moves 2m.

a) applied force.

b) normal force.

c) weight

d) frictional force.

e) the net force

f) what is the value of the coefficient of friction?

Energy à energy is the capacity to do work.
When an object has energy it can do work on itself or its surroundings. THEREFORE, work and energy are related!!!!

When work is done on an object, the energy of the object will change W = ΔE

When the energy of an object changes it is because work was done (by some force) W = ΔE

3. Two cars, A and B, are traveling with the same speed, 20 m/s. Each car then accelerates. Car A (1200-kg) accelerates to 30 m/s and car B (1020 kg) accelerates to 35 m/s. Which car did more work? How much more work?

4. A 55-kg person climbs the stairs (all 2109 of them) to the top of the Sears Tower in Chicago. The total vertical accent of the climb is 443-m. Determine the work done:
a) by the person b) by gravity

5. A 75-kg skier rides a 2830-m long chairlift to the top of a mountain. The lift makes an angle of 14.6° with the horizontal. During the accent determine:
a) the change in the person’s potential energy b) the work done by the lift

c) the work done by gravity.

Conservation of Mechanical Energy à Energy is never created not destroyed; however, it CAN change from one form to another. This includes ALL FORMS of energy.
For mechanical energy we will only consider potential, kinetic and work done by friction (i.e. heat produced)

6.  A particle, starting from point A on a frictionless ramp, is released from rest. It is

Launched upward (due to a vertical turn in the track) to point C.

a)  Determine the speed of the particle at point B.

b)  Determine the height of point C.

7. A rollercoaster is designed (without friction) as shown in the diagram below. If the speed at point A is 5.0 m/s, what is the speed at:

a) point B? b) point C? c) will the coaster reach point D?

8. If the speed of the rollercoaster (shown above) is 10.5m/s at point B, determine the work done by friction (from A to B).
b) if the average angle of incline between points A and B is 40° and the mass of the car is 900-kg, determine the force of friction.

c) Determine the coefficient of friction.

Power à Power is the (time) RATE at which work is done! Because work is a change in energy, power can also be thought of as t he (time) RATE at which energy is transferred.

9. A motor drives a crane that can lift a 700-pound cow to a height of 2 meters. If this takes 12.0-seconds, what is the power of the motor in a) watts? B) horsepower?

10.  Electric energy units are often expressed in the form of kilowatt-hours.

a.  Show that one kilowatt-hour (kWh) is equal to 3.6x106 J.

b.  If the typical family of four in the United States uses electric energy at a rate of 500 W, how many kWh would their electric bill be for one 30 day month?

c.  At the cost of $0.12 per kWh, what would their monthly bill be?

Theory Practice

1.  A slow moving car may have more kinetic energy than a fast moving car. How is this possible?

2.  Determine if each of the following quantities can be positive or negative:
a) work b) power c) potential energy d) kinetic energy

3.  Suppose (neglecting friction) that the kinetic energy of a system decreases. What happens to the potential energy? Give an example of this occurring.
b) Suppose (neglecting friction) that the potential energy of a system decreases. What happens to the kinetic energy? Give an example of this occurring.