Page 10 - TRIAL 2

Power output  mgh Solution
t

25
 4000 9.81   =
15 0.90 = 16.35
 65400W
16.35
= 0.9

E  output  100% =18.17 W
input
0.85  65400
input

input  65400 Revision Exercise
0.85
 76941.18W
Multiple Choice Questions

1. An athlete mass 50 kg uses stairs in 3 m high for
Example 3 workout daily. Calculate the work done by the
A motor takes 6 s to lift a load of 5 kg to a height of
athlete while running up the stairs quickly
2 m.
A. 2461 J
B. 568 J
C. 1471.5 J
motor
D. 1567 J

2. Which of the following statements is true about
load
work done?
A. Work is a vector quantity
2 m B. Work done can be positive or negative
C. Work have same unit as the energy
D. Work is done when a force is applied on
an object.

a) What is the power of the motor?
3. The figure shows a 10N force acting on a block.
The block moves 5m to the right. Calculate the
Solution
work done by the force.
t = 6 s

m = 5 kg

h = 2 m

ℎ
=

A. -50 J
(5)(9.81)(2)
=
6 B. 0 J
= 16.35 W C. 25 J
D. 50 J

b) Find the input power of the motor if the
efficiency is 90 %?
4. A student pulls a 50 kg box up a smooth plane
inclined at 30° to the horizontal as shown in

figure above. If the length of the plane is 5 m,
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