1. Efficiency

2. Efficiency
Real machines are not frictionless. Some of the input energy is dissipated as sound or heat.
The efficiency of a machine is the ratio of useful work output to work input.
The efficiency of an ideal (frictionless) machine is 1, or 100 percent.
The efficiency of real machines is always less than 1.

3. A machine is 75 percent efficient
A machine is 75 percent efficient. If 200 joules of work are put into the machine, how much work output does it produce?

5. The work output is 300 joules for a machine that is 50 percent efficient. What is the work input?

7. A 60-watt light bulb uses 60 joules of electrical energy every second
A 60-watt light bulb uses 60 joules of electrical energy every second. However, only 6 joules of electrical energy is converted into light each second.
What is the efficiency of the light bulb?
What happens to the “lost” energy?

9. A person uses a 75-newton force to push a 51-kilogram car up a ramp
A person uses a 75-newton force to push a 51-kilogram car up a ramp. The ramp is 10 meters long and rises one meter. Calculate the efficiency.

12. Review
An electric motor is used to lift a 0.6 kg mass through a height of 1 m. The energy it uses is measured to be 10 J. Determine the efficiency of the electric motor.