A 2000 W tennis ball machine releases 0.028 kg balls at a speed of - ProProfs Discuss
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A 2000-W tennis ball machine releases 0.028-kg balls at a speed of 100 m/s in 0.20 s. The efficiency of the machine is



A. 70%
B. 14%
C. 28%
D. 1.4%
E. 7.0%

This question is part of thermal physics IB
Asked by Songj, Last updated: Feb 17, 2020

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3 Answers

John Adney

John Adney

Answered Oct 17, 2017

Efficiency = output / input 100, so in this case power output / power input

Power output = W / t, where the work done is the equal to the change in kinetic energy of a ball

Pout = (0.5mv^2 - 0) / t = 0.5 0.028 100^2 / 0.2 = 700 W

efficiency = 700 / 2000 100 = 35%

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 1

kimeuegene

Kimeuegene

Replied on May 30, 2018

Yes, this is correct. It should be fixed by now

Thisuntheekshana

Thisuntheekshana

Answered Jun 22, 2017

Distance =100/0.2=500 work done=500×0.028=14

Power=14J/0.2s=70

Efficiency=70/2000×100%=3.5%

Answer should be 3.5%

 

John Smith

John Smith

Answered Jun 01, 2017

70%
 

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