1. Work Work: using a force for a distance W = F x d
The work done by forces on an object = changes in energy for that object.
Work and Energy are measured in Joules
1 Joule=1 Newton • meter

2. Use the formula Work = Force x distance
42 How much work is performed when a 50 kg crate is pushed 15 m with a force of 20 N?
F 300 J
G 750 J
H 1,000 J
J 15,000 J
Use the formula Work = Force x distance
Force of 20 N x 15 meters = 300 Joules Answer:

3. 6 Types of simple machines
Some Simple Machines:
Inclined planes
Screws
Pulleys
Wheel and axle
Levers
Wedge

4. Why use a machine?
In an ideal (perfect) machine the work put into the machine (Win) = the work put out by that machine (Wout)

5. Machines make work easier
The ideal mechanical advantage of a machine (IMA) of a machine is the number of times the output force is larger than the input force IMA=Fout/Fin
A machine can only make this happen by moving the input force through a farther distance than the output force
Fin • din=Fout • dout

6. 48 The diagram shows an electric motor lifting a 6 N block a distance of 3 m. The total amount of electrical energy used by the motor is 30 J. How much energy does the motor convert to heat? F 9 J G 12 J H 18 J J 21 J

7. Work Input = 30J done by the motor
Work Output = Resistance Force x Resistance Distance
Workout = 18J = 6N x 3m
The difference is lost as heat due to friction, which is 30J – 18J = 12J
Answer G

8. Real Machines use Energy
No real machine is 100 % efficient. i.e. none put out more work than is put in
Efficiency of a machine is work output/work input X 100 %
Eff = Wout X 100%
Win

9. Machines use power
Power: the rate at which energy is used (work is done)
P=Work/time
Power is measured in H.P. or watts
1 watt = 1 Joule
1 sec

10. 45 If a force of 100 newtons was exerted on an object and no work was done, the object must have —
A accelerated rapidly
B remained motionless
C decreased its velocity
D gained momentum
Work = Force x Distance
Work = 0 Force = 100 N so
0 J = 100 N x d
distance must be 0
It did not move!