FA5.1 Efficiency and Power

Get the assessment: FA05.1.docx

Get more Practice Problems: Worksheet-EfficiencyAndPower5.1.docx

The assessment solved:

1. If a heater is 78.0% efficient, how much fuel energy would it consume to provide 120. J of useful heat? How much useful heat could it produce from 360. J of fuel energy?

(154 J, 281 J)

More Examples:

FA5 1 #1a

FA5 1 #2a

2. How much time does it take for a 450. Watt heater to produce 4580 J of heat? What heat will it put out in 32.0 s?

(10.2 s, 14,400 J)

3. What work would you do dragging a 56.5 kg box 12.0 m over a level floor (at a constant low speed) where the coefficient of dynamic friction is 0.215?

(1430 J)

More Examples:

4. What is the minimum power rating a motor could have if it is to lift a 560. kg elevator 35.0 m in 78.0 seconds?

(2460 W)

More Practice Problems: (Get this handout: Worksheet-EfficiencyAndPower5.1.docx)

Efficiency and Power Questions from A5.1

1. a. A heater consumes 125 J of fuel and produces 107 J of useful heat. What is its efficiency? How much fuel would it consume to produce 325 J of useful heat? FA5 1 #1a

b. A motor does 585 J of work in 13.0 seconds. What is its power output? What work could it do in 60.0 seconds? FA5 1 #1b

c. You do 412 J of work dragging a 26.5 kg box over a level floor (at a constant low speed) where the coefficient of dynamic friction is 0.170. What distance did you drag it? FA5 1 #1c

d. What is the minimum time a 540. W motor can lift a 3450 kg land rover 4.50 m? FA5 1 #1d

2. a. A heater is 91.0% efficient. How much useful heat would it produce from 623 J of fuel energy? How much fuel would it consume to produce 371 J of useful heat? FA5 1 #2a

b. A motor does 965 J of work in 12.0 seconds. What is its power output? In what time could it do 1530 J of work? FA5 1 #2b

c. You do 371 J of work lifting a 11.8 kg box. What height did you lift it? FA5 1 #2c

d. What is your power output if you drag a 87.0 kg sled a level distance of 43.0 m in 19.0 s where the coefficient of dynamic friction is 0.210? FA5 1 #2d

3. a. A heater consumes 215 J of fuel and produces 197 J of useful heat. What is its efficiency? How much useful heat would it produce from 645 J of fuel energy?

b. What work does a 420. W motor do in 12.0 seconds? What time would it take the motor to do 758 J of work?

c. You do 850. J of work raising what mass a vertical distance of 8.70 m? FA5 1 #3c

d. A sled dog has a power output of 310. W. In what time can it drag a 112 kg sled 95.0 m across a frozen lake where the coefficient of friction is 0.130? FA5 1 #3d

4. a. A heater is 82.0% efficient. How much fuel would it consume to produce 167 J of useful heat? How much useful heat would it produce from 712 J of fuel energy?

b. A motor does 568 J of work in 11.0 seconds. What is its power output? What work could it do in 135. seconds?

c. You do 381 J of work dragging a box 23.5 m over a level floor (at a constant low speed) where the coefficient of dynamic friction is 0.110. What is the mass of the box? FA5 1 #4c

d. What is the minimum power rating a motor can have if it needs to lift a 2350 kg SUV a vertical distance of 4.50 m in 154 s? FA5 1 #4d

5. a. A heater consumes 618 J of fuel and produces 584 J of useful heat. What is its efficiency? How much fuel would it consume to produce 862. J of useful heat?

b. What work does a 118 W motor do in 16.0 seconds? What time would it take the motor to do 826 J of work?

c. You do 645 J of work dragging a 15.0 kg box over a level floor (at a constant low speed) a distance of 32.0 m. What was the dynamic coefficient of friction? FA5 1 #5c

d. What is the minimum time a 746. W motor can lift a 2770 kg land rover 3.70 m? FA5 1 #5d