Question

Two farmers use an electrically powered elevator to lift bales of hay. All the bales of hay have the same mass. As sunset approaches, they increase the speed of the motor so that more bales are lifted up in a given time. How does this affect the work done in lifting each bale and the useful output power of the motor? Work done in lifting each bale Useful output power of the motor

a. increases decreases

b. increases increases

c. no change decreases

d. no change increases

Answer 1

Answer:

a

Explanation:   work done in short time is when useful power is greatest

Answer 2

The answer is Option d) no change increases

Given:

All the bales have the same mass.

The speed of the motor increases as sunset approaches.

To find:

Affect on work done in lifting each bale and the useful output power of the motor.

Solution:

• Work done is given by the change in potential energy of the bale, which is only dependent on the change in height ie. the amount of height the bale is lifted.
• As this does not change with the speed of the motor, Work done in lifting each bale undergoes no change.
• The Useful output power of the motor also depends on how quickly one bale is lifted.
• As the speed of the motor increases, more bales are lifted in a given time, or one bale is lifted more quickly.
• Hence the Useful output power of the motor increases.

Hence the Work done in lifting each bale undergoes no change while the useful output power increases.

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