Question about Work and Power

[letsgoblue2015]

---

Members don't see this ad.

Question: An object weighing 100 N is traveling horizontally with respect to the surface of the earth in the absence of air resistance at a constant velocity of 5 m/s. What is the power needed?

Answer: 0 W is required to maintain this motion since there is no force component parallel to the direction of displacement, therefore no work is being done and no power is being exerted.

How is there no parallel component if it is travelling horizontally?😕

 

[QrtrLifeCrisis]

Question: An object weighing 100 N is traveling horizontally with respect to the surface of the earth in the absence of air resistance at a constant velocity of 5 m/s. What is the power needed?

Answer: 0 W is required to maintain this motion since there is no force component parallel to the direction of displacement, therefore no work is being done and no power is being exerted.

How is there no parallel component if it is travelling horizontally?😕

What is the power needed to do what? This question stem isn't complete.

 

[rfvbnmju]

Question: An object weighing 100 N is traveling horizontally with respect to the surface of the earth in the absence of air resistance at a constant velocity of 5 m/s. What is the power needed?

Answer: 0 W is required to maintain this motion since there is no force component parallel to the direction of displacement, therefore no work is being done and no power is being exerted.

How is there no parallel component if it is travelling horizontally?😕

Wouldn't constant velocity imply no acceleration so no net force. Without a force, there can't be work. so no power. ??

 

[letsgoblue2015]

Yeah I think you're right. wow ..how did i miss that ****

it's power to maintain motion by the way

 

[letsgoblue2015]

Ok, then what about this question:

An object weighing 100 N 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?

I said 500 W and it's right, but since it's constant velocity, how is there a net force on this one and not on the first question?

Why is this a non-zero answer?

 

[rfvbnmju]

Ok, then what about this question:

An object weighing 100 N 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?

I said 500 W and it's right, but since it's constant velocity, how is there a net force on this one and not on the first question?

Why is this a non-zero answer?

You're doing work against gravity in vertical motion.

 

[QrtrLifeCrisis]

Ok, then what about this question:

An object weighing 100 N 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?

I said 500 W and it's right, but since it's constant velocity, how is there a net force on this one and not on the first question?

Why is this a non-zero answer?

In the first example, there was no force in either direction. That is why the velocity was constant. No force means no work means no power.

In this example, there is gravitational force acting on the objecting pointing downwards at 100N. You would need a 100N force to counteract gravity in order to move upward at a constant velocity. Draw a free body diagram to see this. P = F*v = 100*5 = 500W.

 

[letsgoblue2015]

I thought work is only horizontal?

 

[QrtrLifeCrisis]

Work is defined as force parallel to the motion of the object. Not necessarily horizontal.