Question

SHOW WORK/Explain (need help in bold)

Weight in N = 600N

Weight in lbs. = 132lb

2. Before doing any measurements, estimate how much force your hands are applying to the ground when doing a push up. Estimated Force applied by both hands to the ground = 200 Newton.

3.

Measure how much force your hands actually apply to the ground by one for each hand. Put one hand on the force plate, and another on a book or books at the same height as the scale. Try to keep the force constant. Determine the actual force you apply while doing your pushups. Assume the actual force applied to ground for both hands is simply twice that applied by one hand. Actual force applied by your hands to the ground =199 Newton. How does this compare to your estimated force?

4.

Trials:

Max height for pushup: 33cm

Lowes Height for pushup: 61cm

Distance for pushups: 28 cm

2. Work = 221 N x .28 m = 61.88 Joules

2: Work = 221.2N x .28 m = 61.93 Joules

3: Work = 221N x .28 m = 61.88 Joules

Report your work done as Wave + W : 61.92 J Where W is the half range of the three values.

5. This time we will calculate the power you are expending. The definition of

power is: p=dW dt=work time. To find out how much power you are expanding,

you will need to do at least five push-ups. Note that the work you do will equal

the work up plus the work down. Although it is difficult to prove, the work down

is approximately equal to the work up. So for this (and following) activity,

simply double the work up to get the work down. Now you can calculate power

from the relationship: p=work time

.

Note that units of power are Joules/s = Watts (W)

Work = _______N x __________ m x ________ pushups x 2 = ________Joules

Power = __________ Joules / _________ seconds = __________ Watts

Data and calculations:

1. A food calorie (also known as a kilocalorie) is equal to 4,184 joules. To equal just one food calorie, how many a) Pushups?

Calculations:

2. Actually, you expend far more calories than this! The calculation above assumes that we humans are 100% efficient at doing work. This is far from true…we use less than 25% of food calories to do mechanical work. In other words, for every ten joules of energy we take in from food, we can do 2.5 joules of work and 7.5 joules becomes heat. Given this 25% efficiency, how many pushups and knee bends would you have to do to burn 1 food calorie? # of pushups = ___________

Calculations:

3. Right now, we buy power from the power company at $.15/kw-hr. A kw-hr is equal to 3,600,000 Joules. How many pushups would you have to do to earn $.15 if you were paid at this same rate (hint: you would really get in great shape!)? # of pushups = _____________

Calculations:

Answer 1

For this part, you will need the time that is needed for doing, say 5 push-ups. Let's say it is 't' sec since it is not provided.

Fill in the blanks as below.

Note that units of power are Joules/s = Watts (W)

Work = 221.1 N x 0.28 m x 5 pushups x 2 = 619.08 Joules

Power = 619.08 Joules / t seconds = 619.08/t Watts (You will need to plug in time t needed for 5 push-ups)

1. A food calorie (also known as a kilocalorie) is equal to 4,184 joules. To equal just one food calorie, how many a) Pushups?

Calculations:

We have 5 push-ups = 619.08 Joules

Thus, x push-ups = 4,184 joules

Solving, we will get the number of push-ups needed, x = 33.79 ~ 34 push-ups for burning one food calorie

2. Actually, you expend far more calories than this! The calculation above assumes that we humans are 100% efficient at doing work. This is far from true…we use less than 25% of food calories to do mechanical work. In other words, for every ten joules of energy we take in from food, we can do 2.5 joules of work and 7.5 joules becomes heat. Given this 25% efficiency, how many pushups and knee bends would you have to do to burn 1 food calorie? # of pushups = ___________

Calculations:

Efficiency = Output/Input = 0.25

Thus, Output (For doing push-ups) = 0.25* Input (Food calorie)

Thus for burning one calorie, we will need to do only 25% of above-calculated push-ups.

Thus we will need only 0.25*34 = 8.5 ~ only 9 push ups

3. Right now, we buy power from the power company at $.15/kw-hr. A kw-hr is equal to 3,600,000 Joules. How many pushups would you have to do to earn $.15 if you were paid at this same rate (hint: you would really get in great shape!)? # of pushups = _____________

Calculations:

Again, 5 push-ups generate = 619.08 Joules

Now to get $0.15, you will need to generate 3600000 J (if at all you have a machine that converts your push-ups work into some useful form of energy, like electricity)

Thus, you will need 3600000/619.08*5 = 29075.4 pushups ~ 29076 push ups... Would earn you a really great shape.