CALCULATING POWER
Name:
Date:
Use this worksheet to get extra practice doing the calculations in Math Connect: Using a
Formula to Calculate Power.
 Follow the steps outlined in your textbook.
 Use a calculator to do the calculations.
Equation
power =
energy
E
or P =
time
t
Solve These
1. An instrument uses a battery that provides 500 J of energy for 1200 seconds. What is
the power of the instrument?
What do you know?
power = ____; energy = ____; time = ____
equation to use = ____________________
What do you want to find out?
______________________________________________
Use the formula.
E
P=
=
t
State the power in watts.
___________________________________________________
2. A chainsaw used 4000 J in 180 s. Calculate the power used, in watts.
What do you know?
power = ____; energy = ____; time = ____
equation to use = ____________________
What do you want to find out?
______________________________________________
Use the formula.
E
P=
=
t
State the power in watts.
___________________________________________________
CHAPTER 6
REINFORCEMENT
BLM 6–9
Calculating Power (continued)
3. A diver used 6000 J to dive off a rock cliff. If the diver took 2.5 seconds to reach the
water, how much power was used?
What do you know?
power = ____; energy = ____; time = ____
equation to use = ____________________
What do you want to find out?
______________________________________________
Use the formula.
E
P=
=
t
State the power in watts.
___________________________________________________
4. A battery uses 900 J of energy to run a radio for 25 minutes. What is the power, in
watts, of the radio? Hint: Change the 25 minutes to seconds.
What do you know?
power = ____; energy = ____; time = ____
Convert time to seconds:
equation to use = ____________________
What do you want to find out?
______________________________________________
Use the formula.
E
P=
=
t
State the power in watts.
___________________________________________________
Extend Your Skills
5. Rearrange the formula to calculate energy. If a portable phone needs two watts to
operate and it is used for 15 seconds, how many joules will have been used?
What do you know?
power = ____; energy = ____; time = ____
E
formula to calculate energy. ____________________
t
What do you want to find out?
Rearrange the P =
______________________________________________
Use the formula.
State the energy in joules.
_________________________________________________
CHAPTER 6
REINFORCEMENT
BLM 6–10
Calculating Watt Hours
Name:
Date:
Use this worksheet to get extra practice doing the calculations in Math Connect: Watt
Hours.
 Follow the steps outlined in your textbook.
 Use a calculator to do the calculations.
Equation
Energy = Power x time
or
E = P•t
Solve These
1. An instrument uses 250 000 W in two hours. What is the energy used, in watt hours?
What do you know?
energy = ____; power = ____; time = ____
equation to use = ____________________
What do you want to find out?
______________________________________________
Use the formula.
State the energy in watt hours.
______________________________________________
2. A machine uses 5 000 W in three hours. How much energy was used?
What do you know?
energy = ____; power = ____; time = ____
equation to use = ____________________
What do you want to find out?
______________________________________________
Use the formula.
State the energy in watt hours.
______________________________________________
CHAPTER 6
REINFORCEMENT
BLM 6–10
Calculating Watt Hours (continued)
3. A small toy uses 50 W in half an hour. How much energy was used, in watt hours?
What do you know?
energy = ____; power = ____; time = ____
equation to use = ____________________
What do you want to find out?
______________________________________________
Use the formula.
State the energy in watt hours.
______________________________________________
4. A 100 W light bulb is left on for 24 hours. How much energy was used, in watt hours?
What do you know?
energy = ____; power = ____; time = ____
equation to use = ____________________
What do you want to find out?
______________________________________________
Use the formula.
State the energy in watt hours.
______________________________________________
Extend Your Skills
5. A battery produces 25 W in 60 seconds. How much energy was used, in watt hours?
Hint: Convert the 60 seconds to hours before doing the calculations.
What do you know?
energy = ____; power = ____; time = ____
Convert time to hours:
equation to use = ____________________
What do you want to find out?
______________________________________________
Use the formula.
State the energy in watt hours.
______________________________________________
CHAPTER 6
REINFORCEMENT
BLM 6–11
Calculating Kilowatt Hours
{AB.Sc24.B.K.2.v}{AB.Sc24.B.S.2.ii}{AB.Sc24.B.S.2.i}
Name:
Date:
Use this worksheet to get extra practice doing the calculations in the Math Connect:
Calculating Kilowatt Hours.
 Review the steps outlined in your textbook.
 Fill in the equation and how to convert W•h to kW•h in the space provided.
 Use the steps to help you identify what calculations to do for columns 4 and 5 in the
table below.
 Use a calculator to do the calculations.
 When you have completed your calculations, total the amounts in column 5 to
determine how many kilowatts all of the appliances use together in one month. If you
are not using a calculator, make sure you line up your answers so the decimals are
directly beneath each other. Write the total in the bottom box in column 5.
 Consider the Think About It question that follows. Discuss your ideas with a group.
Write some suggestions in the table provided on the next page.
Equation
What equation do you need to calculate energy? ________________________________
What equation do you need to change W•h to kW•h? ____________________________
Appliance
tabletop fan
240
Average Number
of Hours Used in
a Month
10
dishwasher
1500
45
clothes dryer
2185
90
colour
television
255
45
stereo
100
60
car block heater
600
72
total kilowatt
hours (kW•h)
Power
Rating (W)
Energy Used
in a Month
(W•h)
240 x 10 = 2400
Energy Used
in a Month
(kW•h)
2400
= 2.4
1000