A weightlifter is bench-pressing 65kg. if at full extension the weight is .7m above his chest, then how much has he done after 10 repetitions (given that he simply lets the weights fall back down) if it takes 15 seconds?
To find out how much work the weightlifter has done after 10 repetitions, we need to calculate the total amount of work done in each repetition and then multiply it by the number of repetitions.
The work done by lifting an object is given by the formula: work = force * distance
In this case, the force is equal to the weight being bench-pressed, which is 65 kg. The distance is the height the weight is lifted, which is 0.7 m.
So, the work done in one repetition = 65 kg * 0.7 m
To find out how much work is done after 10 repetitions, we can multiply the work done in one repetition by the number of repetitions.
Total work done = work per repetition * number of repetitions
= (65 kg * 0.7 m) * 10
Next, we need to find out how much time it takes to complete one repetition, given that it takes 15 seconds to complete all 10 repetitions.
The time taken for one repetition = total time / number of repetitions
= 15 seconds / 10
Finally, to calculate the power output of the weightlifter, we need to divide the total work done by the total time taken.
Power = Total work done / Total time taken
Now, let's calculate the work done and power output using the given values:
Work done in one repetition = 65 kg * 0.7 m = 45.5 joules
Total work done = 45.5 joules * 10 = 455 joules
Time taken for one repetition = 15 seconds / 10 = 1.5 seconds
Power output = 455 joules / 1.5 seconds = 303.33 watts
Therefore, the weightlifter has done a total of 455 joules of work after 10 repetitions and has a power output of 303.33 watts.