Power concept related to gravity, constant speed, and air resistance

In summary: I get it now!In summary, the question asks for the applied power required to keep an object weighing 100N moving vertically upwards at a constant velocity of 5 m/s in the absence of air resistance. The equation used to calculate this power is P = Fv, which results in a power of 500W. The total force and total power may be zero due to equal and opposite gravitational power, but the question specifically asks for the applied power.
  • #1
Jmedz4nights
4
0

Homework Statement


An object weighting 100N is traveling vertically upward from the Earth in the absence of air resistance at a constant velocity of 5 m/s. What is the power required to keep the object in motion?


Homework Equations


P = ΔE/t and P = Fvcosθ


The Attempt at a Solution



The explanation given in TPR(the princeton review book) is: since the object's velocity is upward and constant and the force necessary to propel the object is also upward and constant we may use the equation: P = Fv = 100N(5) = 500W.

What I don't understand is this: If the velocity is constant, then the force should be zero, and that should make the Power zero too, right?
 
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  • #2
Welcome to PF!

Hi Jmedz4nights! Welcome to PF! :smile:
Jmedz4nights said:
If the velocity is constant, then the force should be zero, and that should make the Power zero too, right?

If the velocity is constant, then the total force (net force) is zero …

so the total power is zero,

but that's non-zero applied power,

and equal and opposite non-zero gravitational power!

The question is only asking for the applied power. :wink:​
 
  • #3
Thank you tiny-tim! Where in the question stem do you infer applied power, though?
 
  • #4
because it says …
Jmedz4nights said:
What is the power required to keep the object in motion?

… and "power required" obviously means the power we have to add :wink:
 
  • #5
Thank you again all your help, tiny-tim.
 

1. How does gravity affect the power of an object?

Gravity is a force that pulls objects towards each other. The power of an object is determined by its mass and acceleration. In the case of gravity, the acceleration is due to the force of gravity. The greater the mass of an object, the greater its gravitational pull and therefore the greater its power.

2. How does constant speed affect the power of an object?

Constant speed means that the object is moving at a steady rate without changing its velocity. In this case, the power of the object remains constant. This is because power is a measure of how quickly work is being done, and for constant speed, the work being done is constant.

3. How does air resistance affect the power of an object?

Air resistance is a force that opposes the motion of an object through air. As an object moves through air, it experiences a drag force that reduces its speed and power. The amount of air resistance depends on the size and shape of the object and the density of the air. The greater the air resistance, the lower the power of the object.

4. How do gravity, constant speed, and air resistance work together to affect the power of an object?

Gravity, constant speed, and air resistance all play a role in determining the power of an object. Gravity determines the initial acceleration of the object, constant speed keeps the power constant, and air resistance acts as a resistive force that decreases the power of the object. Together, they determine the overall power of the object in motion.

5. How can we calculate the power of an object taking into account gravity, constant speed, and air resistance?

The formula for power is P = W/t, where P is power, W is work, and t is time. To calculate the power of an object in motion, we need to first calculate the work being done, which is equal to the force applied multiplied by the distance moved. In the case of gravity, this would be the weight of the object multiplied by the distance it falls. Then, we divide the work by the time it takes for the object to move that distance. This will give us the power, taking into account the effects of gravity, constant speed, and air resistance.

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