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An engineer wants to design an improved elevator for a building The original design used a motor that could lift 1000 kg through a distance of 20 meters in 30 seconds. The engineer wants a motor that can lift 800 kg through a distance of 30 meters in 20 seconds. Compared to the old motor, the new motor (A) should exert a force of the same magnitude, but must provide a larger power output. (B) should exert a force of a larger magnitude, and must provide a larger power output. (C) can exert a force of a smaller magnitude, and can provide the same power output. (D) can exert a force of a smaller magnitude, but must provide a larger power output. (E) can exert a force of a smaller magnitude, but must provide a larger power output.

An engineer wants to design an improved elevator for a building The original design used a motor that could lift 1000 kg through a distance of 20 meters in 30 seconds. The engineer wants a motor that can lift 800 kg through a distance of 30 meters in 20 seconds. Compared to the old motor, the new motor
(A) should exert a force of the same magnitude, but must provide a larger power output.
(B) should exert a force of a larger magnitude, and must provide a larger power output.
(C) can exert a force of a smaller magnitude, and can provide the same power output.
(D) can exert a force of a smaller magnitude, but must provide a larger power output.
(E) can exert a force of a smaller magnitude, but must provide a larger power output.

Grade:upto college level

1 Answers

Deepak Patra
askIITians Faculty 471 Points
8 years ago
Earth revolves around the Sun in a perfectly circular orbit. The displacement of the Earth in the circular motion around the Sun is along the tangent to the orbit whereas the force of Sun is along the radius vector of the circle. These two vectors will be orthogonal to each other that mean both the vector will make 90̊ to each other.
Since work done by the force F on an object which is displaced by a distance s is defined as,
W = F. s
= Fs cos ϕ …… (1)
Where ϕ is the angle between F and s and here the value of ϕ is 90̊ .
So, cos ϕ = cos 90̊
= 0 …… (2)
Putting the value of equation (2) in equation (1),
W = F. s
= Fs cos ϕ
= (Fs) (0)
= 0 …… (3)
From equation (3) we observed that, the work done by the Sun on the Earth will be zero.

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