work and power

by Shari Tahririan & Leo Vialet December 21th

• Symbols
• Definitions
• Formulas
• General Problem Solving Strategy
• Example Problems : Work, Work and Weight, Power

• Work and Power worksheet solutions

Here's are the new Symbols introduced for Work and Power: :

W work

P Power

KE Kinetic Energy

Pe Gravitational Potential Energy





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Work: work is the measure of hte change, a force gives rises to when it
acts on something. When an object is displaced while a force acts on it, the work done
by the force is equal to the product of the displacement and the componemt of the
force in the direction of the displacement. The SI unit of Work is the Joule (J).

Power: Rate at which Work is being done

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Here are the formulas you are going to need to be able to solve Work and Power type of

problems:

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1. Read the problem.
2. Organize the data you have
3. Find the formulas you are going to use
4. Replace the letters by numbers
5. Solve for the missing number

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1. How much work does Fred do exerting 45 N to lift a box 3.2 m?

 

First you have to write down what you know :

F = 45N, x = 3.2 m

Then look at the formulas to know which one you are going to use :

W = Fx

After that letís substitute in the number and finishing the problem :

W = 45 * 3.2

W = 144 Joules

2. What distance will 90 J of energy slide a box against 12 N of frictional force?

 

First, letís write down the data we have :

W = 90 J, F= 12 N

Then letís look at the formulas to know which one to use :

W = Fx

After that letís substitute in the number and finishing the problem :

90 = 12 x,

x= 90/12,

x = 7.5 meters

3. . Katherine moves a box 7.2 m doing 9 J of work. What is the fricitonal force?

First, letís write down the data we have :

Then letís look at the formulas to know which one to use :

After that letís substitute in the number and finishing the problem :

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1. . How much work is needed to lift a 45 Kg box 9.2 m?

 

First, letís write down the data we have 

m = 45 Kg, h = 9.2 meters

Then letís look at the formulas to know which one to use :

w= mg, W = wh

After that letís substitute in the number and finishing the problem :

w=45 * 9.8

= 441 N

W = 441 * 9.2

W = 4060 Joules

2. A pump does 4500 J of work in a minute. What mass of water can it pump to a height of 4.5 m in one minute?

 

First, letís write down the data we have 

W = 4500J, h = 4.5 meters

Then letís look at the formulas to know which one to use :

W = wh, w = mg

After that letís substitute in the number and finishing the problem 

4500 = w * 4.5

w = 4500/4.5

w = 1000 N

w = m g

1000 = m * 9.8

m = 1000/9.8

m = 102 kg

3. A rifle cartridge contains 250 J of energy. How far can it launch its 60 grams slug into the air if it is shot straight up?

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1. A motor can do 540 J of work in 9.0 seconds. What's its power output?

 

First, letís write down the data we have :

W = 540 J, t = 9.0 s

Then letís look at the formulas to know which one to use :

P = W/t

After that letís substitute in the number and finishing the problem :

P = 540 /9.0

P= 60 Watts

2. In what time can a 250 W motor do 4500 J of work?

 

First, letís write down the data we have : 

P = 250 Watts, W = 4500 Joules

Then letís look at the formulas to know which one to use :

P = W/t

After that letís substitute in the number and finishing the problem :

250 = 9500 / t

t = 9500/250

t = 38s

3. How much work does a 25 W motor do in 5 minutes?
   

First, letís write down the data we have : 

Then letís look at the formulas to know which one to use :

After that letís substitute in the number and finishing the problem :

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