Why Is Average Thermal Power Not Negative in This Friction Scenario?

AI Thread Summary
The discussion clarifies that average thermal power is not negative in the friction scenario because it measures thermal power produced rather than work done on the rock. The friction force acts in the same direction as the rock's velocity, which influences the power calculation. The average power is derived from the product of the friction force and the average velocity. This distinction between thermal power and work is crucial for understanding the scenario. Overall, the confusion arises from the interpretation of forces and their directions in relation to power calculations.
yashboi123
Messages
17
Reaction score
0
Homework Statement
A 20.0 kg rock is sliding on a rough, horizontal surface at 8.00 m/s and eventually stops due to friction. The coefficient of kinetic friction between the rock and the surface is 0.200.
Relevant Equations
P = F . v
P = Fvcos(x)
1696561568154.png


I'm curious as to why the average power is not negative in this scenario, since I thought the friction force is in the opposite direction of velocity. As far as I see friction force is the only acting force in the problem, but I may be wrong. I solved this by simply doing (Friction Force * (v/2)), the average velocity.
 
Physics news on Phys.org
yashboi123 said:
I'm curious as to why the average power is not negative in this scenario
Because it asks for the thermal power produced, not the work per unit time done on the rock. The friction force the rock exerts on the surface is in the same direction as its velocity.
 

Thread 'Rolling without slipping on a curved surface'

Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
View full post »
Thread 'Voltmeter readings for this circuit with switches'

Thread 'Voltmeter readings for this circuit with switches'

TL;DR Summary: I would like to know the voltmeter readings on the two resistors separately in the picture in the following cases , When one of the keys is closed When both of them are opened (Knowing that the battery has negligible internal resistance) My thoughts for the first case , one of them must be 12 volt while the other is 0 The second case we'll I think both voltmeter readings should be 12 volt since they are both parallel to the battery and they involve the key within what the...
View full post »
Thread 'Trying to understand the logic behind adding vectors with an angle between them'

Thread 'Trying to understand the logic behind adding vectors with an angle between them'

My initial calculation was to subtract V1 from V2 to show that from the perspective of the second aircraft the first one is -300km/h. So i checked with ChatGPT and it said I cant just subtract them because I have an angle between them. So I dont understand the reasoning of it. Like why should a velocity be dependent on an angle? I was thinking about how it would look like if the planes where parallel to each other, and then how it look like if one is turning away and I dont see it. Since...
View full post »

Similar threads

Momentum: instantaneous or average?
Replies
9
Views
1K
Block drifts off between two moving planes through friction
Replies
21
Views
842
For the friction formula when to use Fn(normal force)×mu and when F×mu
Replies
17
Views
2K
Friction force on a ball falling through a body of water
Replies
9
Views
1K
Why is the direction of kinetic/static friction up a ramp?
Replies
7
Views
1K
Is it friction or tension acting on the person hanging on a rope?
Replies
4
Views
1K
How can we model a rolling truck on an incline using rotational motion analysis?
Replies
24
Views
2K
Thermal energy dissipated from the brakes in a car
Replies
28
Views
2K
Two bars connected by a spring on a floor with friction
Replies
37
Views
1K
Calculate Distance Traveled: Instantaneous vs. Average Velocity
Replies
5
Views
2K

Hot Threads

Recent Insights

Back
Top