# Physics Experiment

• Sep 27th 2012, 11:47 AM
Louisana1
Physics Experiment
During a physics experiment, a fan is used to apply a push to a cart on a hortizontal track. A student would like the net force on the cart to be 12 N to the left. The student knows that the friction force on the cart by the track will be 3 N to the left. The fan should exert a force of

A. 15 N to the right
B. 15 N to the left
C 9 N to the right
D 9 N to the left
E None of these
• Sep 27th 2012, 12:16 PM
Oldspice1212
Re: Physics Experiment
Well what have you got so far?
• Sep 27th 2012, 12:20 PM
Louisana1
Re: Physics Experiment
all going left 15
• Sep 27th 2012, 12:25 PM
MarkFL
Re: Physics Experiment
If there is a net force of 12 N to the left on the cart, meaning it will move to the left, the force of kinetic friction will oppose the motion, that is, will point to the right.

Did you give the problem exactly as stated? Normally, friction does not contribute to motion, but rather retards it.
• Sep 27th 2012, 12:26 PM
Louisana1
Re: Physics Experiment
Yes that is the question
• Sep 27th 2012, 12:28 PM
Louisana1
Re: Physics Experiment
there was a typo
During a physics experiment a fan is used to apply a push to a cart on a horizontal track. A student would like the net force on the cart to be 12 N to the right. The student knows that the friction force on the cart by the track will be 3 n to the left.
• Sep 27th 2012, 12:38 PM
MarkFL
Re: Physics Experiment
If we choose to the right to be positive, we may then state:

$F_{\text{net}}=F_{\text{fan}}-f_{k}$

$F_{\text{fan}}=F_{\text{net}}+f_{k}$

We are told we want/have:

$F_{\text{net}}=12\text{ N}$

$f_{k}=3\text{ N}$

Thus, we have:

$F_{\text{fan}}=12\text{ N}+3\text{ N}=15\text{ N}$

Since this is positive, we know it is to the right by our definition.