How Do Power, Force, and Velocity Interact?

[hello478]

Homework Statement

question c part ii) power produced by engine

Relevant Equations

p= f* v

 

[BvU]

8628.46 ?

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[hello478]

8628.46 ?

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its by finding the component of weight along slope

 

[BvU]

So the slope is given, and so is the mass of the lorry. Given for you , that is.
But my telepathic capabilities are limited and I need a complete problem statement, typed out.

And: what are the directions of 8628.46 and the resistive force ?

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[hello478]

So the slope is given, and so is the mass of the lorry. Given for you , that is.
But my telepathic capabilities are limited and I need a complete problem statement, typed out.

And: what are the directions of 8628.46 and the resistive force ?

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i have attached the question image above..., is it not there? let me check again

 

[haruspex]

Homework Statement: question c part ii) power produced by engine
Relevant Equations: p= f* v

View attachment 342385
View attachment 342389

The F you need to use in P=Fv is the motive force delivered by the engine. This has to balance the opposing forces, the 5200N of resistance plus the gravitational component.

 

[hello478]

The F you need to use in P=Fv is the motive force delivered by the engine. This has to balance the opposing forces, the 5200N of resistance plus the gravitational component.

ok so in p=fv
the f would always be total force?

 

[haruspex]

ok so in p=fv
the f would always be total force?

Depends what you mean by "total force". As you wrote, since the speed is constant the total force on the truck is zero.

 

[hello478]

Depends what you mean by "total force". As you wrote, since the speed is constant the total force on the truck is zero.

yeah the net force would be zero
but here... we would have to use the force which is causing the body to move(the total force, sum of resistive forces) with that velocity???
is this explanation fine?

 

[haruspex]

yeah the net force would be zero
but here... we would have to use the force which is causing the body to move

Yes, that being the static frictional force on the tyres. We can consider that the motive force provided by the engine, though in reality what the engine provides is a torque.

(the total force, sum of resistive forces) with that velocity???
is this explanation fine?

Not sure what you mean by that. In the general case the truck is accelerating, so we have $F_{net}=F_{static}+F_{resist}=ma$, $F_{resist}$ being negative. So the engine power would be $F_{static}v=(ma-F_{resist})v$.

 

[hello478]

Not sure what you mean by that.

i meant that we would multiply the force which causes to move the lorry with the velocity it creates
also is this applicable to all cases?

 

[haruspex]

i meant that we would multiply the force which causes to move the lorry with the velocity it creates

You don't have to care what creates the velocity. What matters is that a force $\vec F$ is exerted at a point on a body while that point is moving with velocity $\vec v$. The power transferred is $\vec F\cdot\vec v$.

 

[BvU]

I'm still worried about the signs:

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[hello478]

F would be 8628.46+5200

 

[BvU]

I agree