3. Reducing friction in a machine
A decreases its actual mechanical advantage
B decreases its work output
C increases its efficiency
D increases its ideal mechanical advantage
4. The efficiency of a machine is always less than 100 percent because
A a machine cannot have an IMA (ideal mechanical advantage) greater than one
B some work is lost to friction
C the work input is too small
D the work output is too great
5. A motor with an efficiency of 75% must supply 240 J of useful work. What amount of work must be supplied to the motor?
A 75 J
B 180 J
C 320 J
D 420 J

C

B

C

Explanation:

To increase the efficiency of a machine, it is advisable that one reduces friction within the machine parts as much as possible through common procedures such as greasing and oiling. This is helps to reduce the amount of energy lost due to friction hence contributing to output which finally is useful in calculating efficiency of a machine.

Efficiency can't be 100% since it is found by dividing work output verses input but the output is usually slightly less than the input energy due to energy losses within a machine. The losses that occur are mainly attributed to frictional losses.

Here efdiciency and work output are given but input is missing. Converting efficiency into decimal we have 0.75 and since efficiency=output/input then the input will be given by output/efficiency and by substitution 240/0.75=320 J

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the device is called “ rocket engine”