Efficiency Quiz

In an ideal simple machine, what does the law of conservation of energy predict?

• The amount of work done by the machine or on the machine are equal.

• The machine does less work than the input work.

According to the second law of thermodynamics, no process is 100% efficient. What can be true about the reasons why the work done is always less than the input work in a real block and tackle system while lifting the weight?

• Friction force reduces efficiency and therefore transforms some of the useful input energy into heat.

• The machine does not lose any energy to heat.

What is the formula for calculating the efficiency of a simple machine?

• efficiency = output work / input work x 100%

• efficiency = (output work - input work) x 100%

Which of these equations is correct?

Tags

NGSS.MS-PS3-5

A car transfers 100 J of chemical energy in order to gain 50 J of kinetic energy. The efficiency of the car is

• 50%

• 200%

Tags

NGSS.MS-PS3-5

This car needs 8600J of energy to power it. If 5000J is changed into useful energy, how much energy is wasted?

• 3600J

• 5000J

Tags

NGSS.MS-PS3-4

NGSS.MS-PS3-5

Reason why machines cannot run 100% efficiently.

• magic
• friction

Tags

NGSS.MS-PS3-5

This car needs 8600J of energy to power it. If 5000J is changed into useful energy, how much energy is wasted?

• 13600J

• 3600J

• 5000J

• 8600J

Tags

NGSS.MS-PS3-1

NGSS.MS-PS3-5

What is the work output of a machine that has a work input of 2,800 Joules and an efficiency of 90%?

• 25200 J

• 2520 J