A \(62-\mathrm{kg}\) woman takes \(6.0 \mathrm{s}\) to run up a flight of stairs. The landing at the top of the stairs is \(5.0 \mathrm{m}\) above her starting place. (a) What is the woman's average power output while she is running? (b) Would that be equal to her average power input-the rate at which chemical energy in food or stored fat is used? Why or why not?

Short Answer

Expert verified
Answer: The woman's average power output while running up the stairs is 507 W. This is not equal to her average power input, as some of her body's stored energy is lost as heat and used for other purposes.

Step by step solution

01

Calculate the work done by the woman while running up the stairs

First, we will find the gravitational potential energy gained by the woman as she climbs the stairs. We can find this using the formula: \(PE = m \cdot g \cdot h\) where \(PE\) is the potential energy, \(m\) is her mass, \(g\) is gravitational acceleration (\(9.8 \, m/s^2\)), and \(h\) is the height of the stairs. Plugging in the given values: \(PE = 62 \, kg * 9.8 \, m/s^2 * 5.0 \, m\)
02

Calculate the gravitational potential energy

Now we can calculate the gravitational potential energy: \(PE = 62 \, kg * 9.8 \, m/s^2 * 5.0 \, m = 3042 \, J\) (joules)
03

Calculate the average power output

Now that we have the work done (potential energy gained), we can find the average power output by dividing it by the time taken: \(P_\text{out} = \frac{PE}{t}\) \(P_\text{out} = \frac{3042 \, J}{6.0 \, s}\)
04

Solve for average power output

Now we can solve for average power output: \(P_\text{out} = \frac{3042 \, J}{6.0 \, s} = 507 W\)
05

Average power input

Now let's discuss the average power input. The woman's body uses chemical energy stored in the form of food or fat. The average power output represents the rate at which this energy is converted into work to climb the stairs. However, not all of the energy stored in the body is used for this purpose - some energy is lost as heat, and some might be used for other bodily activities. Therefore, we can conclude that the average power input will be higher than the average power output found in Step 4. To summarize: - (a) The woman's average power output while running up the stairs is 507 W. - (b) That would not be equal to her average power input, as some of her body's stored energy is lost as heat and used for other purposes.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Prove that \(U=-2 K\) for any gravitational circular orbit. [Hint: Use Newton's second law to relate the gravitational force to the acceleration required to maintain uniform circular motion.]
A \(1500-\mathrm{kg}\) car coasts in neutral down a \(2.0^{\circ}\) hill. The car attains a terminal speed of \(20.0 \mathrm{m} / \mathrm{s} .\) (a) How much power must the engine deliver to drive the car on a level road at $20.0 \mathrm{m} / \mathrm{s} ?$ (b) If the maximum useful power that can be delivered by the engine is \(40.0 \mathrm{kW},\) what is the steepest hill the car can climb at \(20.0 \mathrm{m} / \mathrm{s} ?\)
An airline executive decides to economize by reducing the amount of fuel required for long-distance flights. He orders the ground crew to remove the paint from the outer surface of each plane. The paint removed from a single plane has a mass of approximately \(100 \mathrm{kg} .\) (a) If the airplane cruises at an altitude of \(12000 \mathrm{m},\) how much energy is saved in not having to lift the paint to that altitude? (b) How much energy is saved by not having to move that amount of paint from rest to a cruising speed of $250 \mathrm{m} / \mathrm{s} ?$
Use dimensional analysis to show that the electric power output of a wind turbine is proportional to the cube of the wind speed. The relevant quantities on which the power can depend are the length \(L\) of the rotor blades, the density \(\rho\) of air (SI units \(\mathrm{kg} / \mathrm{m}^{3}\) ), and the wind speed \(v\).
The orbit of Halley's comet around the Sun is a long thin ellipse. At its aphelion (point farthest from the Sun), the comet is $5.3 \times 10^{12} \mathrm{m}\( from the Sun and moves with a speed of \)10.0 \mathrm{km} / \mathrm{s} .$ What is the comet's speed at its perihelion (closest approach to the Sun) where its distance from the Sun is \(8.9 \times 10^{10} \mathrm{m} ?\)
See all solutions

Recommended explanations on Physics Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free