Answer:
80%
Explanation:

800 / 1000 = 0.8
Efficiency = 0.8 *100 = 80%
Satellite. think of the moon.
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Answer:
W = 0 :The work done on the wall is zero,because the wall is not moving
Explanation:
Work theory
Work is the product of a force applied to a body and the displacement of the body in the direction of this force.
W= F*d Formula (1)
W: Work (Joules) (J)
F: force applied (N)
d=displacement of the body (m)
The work is positive (W+) if the force goes in the same direction of movement.
The work is negative (W-)if the force goes in the opposite direction to the movement
Data
F= 400-N
d= 0
Problem development
We apply formula (1) to calculate the work done on the wall:
W= 400*0
W=0