Efficiency is defined as the measure of the amount of work or energy is conserved in a certain process. At all times, in every process, work or energy is always lost or wasted due to certain interference. Not all work given is converted to useful work or energy. Thus , efficiency is calculated by dividing the energy or work output to the energy or work input then the value is multiplied by 100 to express efficiency as percentage.
Efficiency = work output / work input
Efficiency = (1020 J / 1200 J) = 85%
Answer:

Explanation:
We can try writing the equation of the horizontal component of the length of the minute hand in terms of distance and the angle, that depends of time in this particular case.
The x-component of the length of the minute hand is:
(1)
- d is the length of the minute hand (d=D/2)
- D is the diameter of the clock
- t is the time (min)
Now, using the angular kinematic equations we can express the angle in term of angular velocity and time. As we know, the minute hand moves with a constant angular velocity, so we can use this equation:
(2)
Also we know, that the minute hand moves 90 degrees or π/2 rad in 15 min, so using the definition of angular velocity, we have:
Now, let's put this value on (2)
Finally the length x(t) of the shadow of the minute hand as a function of time t, will be:

I hope it helps you!
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