Net Force on a Stalled Car Being Pushed Up a Hill?

[physicsgurl12]

Homework Statement

A stalled car is being pushed up a hill by 3 people and it is moving at a constant speed the net forcce on the car is
a in the opposite of the cars motion
b in the same direction as the cars motion-wrong
c zero
d none of the above

Homework Equations

noone

The Attempt at a Solution

is it c zero because there's gravity and the normal force from the hill?

 

[SammyS]

How do you know that these forces cancel each other completely?

 

[physicsgurl12]

i don't?

 

[SammyS]

You should. One (or two) of Newton's Laws tells you why.
...

If they don't cancel, then the net force isn't zero.

 

[physicsgurl12]

because there opposie and equal forces?

 

[DaveC426913]

What do you know about the net force acting upon an object that is moving with constant velocity?

 

[SammyS]

But how do you know they're opposite & equal. There's something in the problem that should tell you.

(One of Newton's Laws)

 

[physicsgurl12]

that its a constant speed?

 

[DaveC426913]

that its a constant speed?

And what does that tell you about the forces acting on it, specifically the net force?

 

[SammyS]

that its a constant speed?

Answer Dave's question by using Newton's Second Law.

 

[physicsgurl12]

f=ma
so the forces =0 because if there is constant speed there's no acceleration

 

[SammyS]

We'll assume it's moving in a straight line, so constant sped means constant velocity.

Yes, that's why you know the net force is zero ! The reason it's zero is that the forces cancel. Kind of a picky point here, but it could be important for understanding what's going on.

 

[physicsgurl12]

okay thanks