Here's the question and my answer doesn't match what the book gives as you can see in the below workings out(adsbygoogle = window.adsbygoogle || []).push({});

1)A 300 KG weight is lifted with a block and tackle to a height of 4m in 1 minute and 20 seconds A) Neglecting friction, calculate the power used? B)What’s the efficiency if the actual power used is 24KW?

My working a) Power=work/time To find work firstly force must be found

Force=300 KG X 9.81m/s= 2,943 N

Work=Force X Distance= 2,943 N X 4M=11,772 Joules

Power=11,772/60 seconds=196.2 Watts

B)Efficiency=Power out/Power in X 100

196.2/24000 X 100

Book answers= A)=15W B)=62 percent

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# Problem question on power calculation

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