Problem question on power calculation

So the correct power used is 11,772/80 seconds = 147.15 Watts and the efficiency is 147.15/24000 X 100 = 0.613125 or 61.3%.In summary, the conversation discusses the calculation of power and efficiency in lifting a 300 KG weight using a block and tackle. The correct power used is 147.15 Watts and the efficiency is 61.3%. The book answers of 15W and 62% are incorrect due to incorrect use of time in the calculation.
  • #1
Here's the question and my answer doesn't match what the book gives as you can see in the below workings out

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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  • #2
are you sure your data is correct? your working is correct except for the part where you should have put 80 instead of 60 seconds. plus the part about 15 W and 24 KW doesn't match...
  • #3
yep those are the answers the book gives. Why would I divide by 80 seconds and not 60?
  • #4
wewelsburg said:
yep those are the answers the book gives. Why would I divide by 80 seconds and not 60?

Because the work is done "in 1 minute and 20 seconds" = 60sec+20sec = 80sec.

1. What is power calculation and why is it important in scientific research?

Power calculation is a statistical method used to determine the minimum sample size needed for a study to detect a significant effect. It is important because it ensures that a study has enough statistical power to detect a true effect, thus increasing the reliability and validity of the research findings.

2. How is power calculation performed?

Power calculation involves several factors such as the desired significance level, effect size, and sample size. It is typically performed using statistical software or online calculators, which take these factors into account to determine the required sample size for a study.

3. What is the significance level in power calculation?

The significance level, also known as alpha, is the probability of rejecting the null hypothesis when it is actually true. In power calculation, it is typically set at 0.05, which means there is a 5% chance of rejecting the null hypothesis even if it is true. This is the standard level used in most scientific research.

4. What is an effect size and how does it impact power calculation?

Effect size is a measure of the magnitude of the difference or relationship between variables in a study. It can be calculated in various ways depending on the type of analysis being conducted. A larger effect size indicates a stronger relationship or difference between variables, and therefore requires a smaller sample size to achieve sufficient statistical power.

5. Can power calculation be performed after a study has been conducted?

Ideally, power calculation should be performed before a study is conducted to determine the appropriate sample size. However, it can also be performed after a study has been conducted to assess the power of the study and determine if the sample size was sufficient. This can provide valuable information for future research studies.

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