The efficiency of the device is 30 %
Explanation:
The efficiency of a heat engine is given by:
where
W is the work done by the engine
is the heat in input to the engine
For the device in this problem, we have:
W = 120 J is the work done
is the heat in input
Substituting, we find the efficiency:
which corresponds to an efficiency of 30%.
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The hang time of the ball is 4.08 s
Explanation:
The ball is in free fall motion: this means that it is acted upon gravity only, so its acceleration is the acceleration of gravity,
downward (the negative sign refers to the downward direction).
Since this is a uniformly accelerated motion, we can solve the problem by using the following suvat equation:
where
v is the final velocity
u is the initial velocity
a is the acceleration
t is the time
First we calculate the time it takes for the ball to reach the maximum height, where the velocity is zero:
v = 0
Substituting:
u = +20 m/s
we find t
The motion of the ball is symmetrical, so the total time of flight is just twice the time needed to reach the maximum height, therefore:
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