1000 kW of power is supplied to a motor. 90% of this is transmitted to a machine operating at 80% efficiency. The machine lifts an object of 10-tons with a velocity _____ m/s. (Assume g = 10m/s^2)

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Editor">Editor Staff asked 1 year ago

1000 kW of power is supplied to a motor. 90% of this is transmitted to a machine operating at 80% efficiency. The machine lifts an object of 10-tons with a velocity _____ m/s. (Assume g = 10m/s^2)
 
(a) 2
 
(b) 4
 
(c) 6
 
(d) 8
 
The question was asked in my homework.
 
This question is from Power in chapter Work, Energy and Power of Physics – Class 11
Select the correct answer from above options 
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Editor">Editor Staff answered 1 year ago

Correct answer is (c) 6
 
Easiest explanation: Power transmitted to machine = (90/100) x (1000) kW
 
 = 900 kW
 
Power used to lift object = (80/100) x 900 KW
 
 = 720 kW
 
7,20,000 = F x v
 
 = (1/2 x m x v^2) x v
 
 = 10,000/2 x v^3
 
v^3 = 216
 
v = 6 m/s.

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