Analyzing Forces on a Car Attached to a Wall with a Rope

[John_tawil]

Homework Statement

A rope is attached to a wall on one end and to a car on the other end. Someone pushes up on the rope and the car starts to move when the rope makes an angle of 5^o with the floor. M_car=2500kg

Homework Equations

ΣF_x=ma
ΣF_y=ma

The Attempt at a Solution

Look at the car and the rope separately.

I'm assuming the car has;
ΣF_x=ma
ΣF_y= 0
and the rope has the opposite;
ΣF_x= 0
ΣF_y= ma

But I'm not getting anywhere? Am I doing it right?

 

[sophiecentaur]

You seems to be mixing up your x and y directions. (And so was i, because I was trying to read the printing laying on its side.)
The only force on the car that's accelerating it is horizontal. The trig will tell you what it is at 5^o.
But I don't see how there would be any lower limit to the force needed if there is no friction.

 

[Doc Al]

But I'm not getting anywhere? Am I doing it right?

Nothing is accelerating here. (Not yet, anyway.)

Start by identifying the forces acting on the truck.

 

[Doc Al]

But I don't see how there would be any lower limit to the force needed if there is no friction.

Oops... I didn't notice that it said no friction. (Missed that when trying to read sideways.)

I don't get the point of the problem. With no friction, you need not be a muscleman to move the truck. A fly could do it.

 

[sophiecentaur]

Oops... I didn't notice that it said no friction. (Missed that when trying to read sideways.)

I don't get the point of the problem. With no friction, you need not be a muscleman to move the truck. A fly could do it.

A touch of the "badly written questions' disease, I think.

 

[John_tawil]

So would you need 1N of force up to push to the left?

 

[sophiecentaur]

So would you need 1N of force up to push to the left?

If there's no friction, 1microNewton would produce finite acceleration. The question appears to be flawed - or it's angled to make you spot the nonsense aspect of it.

 

[Doc Al]

A touch of the "badly written questions' disease, I think.

Indeed.