Book M Ch 4 Formula Quiz

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This is a pop quiz over the formulas we've been using in this chapter. All answers will be in the nearest WHOLE number , not tenths. Put ONLY the numbers in, not the units (such as Joules or Watts).

• 1.

How much power is needed to cut a lawn in 50 minutes if the work involved is 100,000J? Hint: you must convert minutes to seconds. 50 minutes times 60 seconds ? ___Watts (put only the numeric value to the nearest WHOLE number).

Explanation
To calculate the power needed to cut the lawn, we need to divide the work involved by the time it takes to complete the task. First, we convert 50 minutes to seconds by multiplying it by 60, which gives us 3000 seconds. Then, we divide the work of 100,000J by the time of 3000 seconds. The result is 33.3 watts. Since we are asked to put only the numeric value to the nearest whole number, the answer is 33 watts.

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• 2.

As you push a lawn mover, the horizontal force is 300 N. If you push the mower a distance of 500 M, how much work do you do?  _____ J

Explanation
The work done is calculated by multiplying the force applied by the distance covered. In this case, the force applied is 300 N and the distance covered is 500 M. Therefore, the work done is 300 N * 500 M = 150,000 J or 150000 J.

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• 3.

A librarian lifts a box of books that weighs 93 N a distance of 1.5 m. How much work does she do? ____J

Explanation
The work done by the librarian can be calculated using the formula: work = force × distance. In this case, the librarian lifted a box of books that weighed 93 N (force) a distance of 1.5 m. Therefore, the work done is 93 N × 1.5 m = 139.5 J. Since work is typically rounded to the nearest whole number, the answer would be 140 J.

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• 4.

A teacher does 140 J of work in 20 s. How much power did he use?  ____W

Explanation
The power used by the teacher can be calculated using the formula: Power = Work / Time. In this case, the work done by the teacher is 140 J and the time taken is 20 s. Substituting these values into the formula, we get Power = 140 J / 20 s = 7 W. Therefore, the teacher used 7 watts of power.

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• 5.

You do 100 J of work in pulling out a nail with a claw hammer. If the hammer does 70 J of work, what is the hammer's efficiency? ______%

Explanation
The efficiency of a machine is calculated by dividing the useful output work by the input work and multiplying by 100%. In this case, the useful output work is 70 J, which is the work done by the hammer. The input work is 100 J, which is the total work done in pulling out the nail. Therefore, the efficiency of the hammer can be calculated as (70 J / 100 J) * 100% = 70%.

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• 6.

Find the efficiency of a machine if the input work is 150 J and the output work is 90 J.  _____%

Explanation
Efficiency is calculated by dividing the output work by the input work and multiplying by 100. In this case, the output work is 90 J and the input work is 150 J. Dividing 90 by 150 gives us 0.6. Multiplying 0.6 by 100 gives us 60%. Therefore, the efficiency of the machine is 60%.

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• 7.

To lift a crate, a pulley system exerts a force of 2,750 N. Find the mechanical advantage of the pulley system if the input force is 250 N.  ____

Explanation
The mechanical advantage of a pulley system is calculated by dividing the output force by the input force. In this case, the output force is 2,750 N and the input force is 250 N. Therefore, the mechanical advantage is 2,750 N / 250 N = 11.

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