# Friction problem

• Nov 2nd 2012, 02:33 AM
mysur
Friction problem
A shopper picks up a 2kg packet of pasta with the thumb and index finger of one hand. The coef of friction between his fingers and the wrapping is 0.3. What horizontal force must he exert to prevent the packet from slipping?

2sin30*0.3 ( angle betweenfingers and wrapping) not sure help me out
• Nov 2nd 2012, 03:39 AM
fkf
Re: Friction problem
Quote:

Originally Posted by mysur
A shopper picks up a 2kg packet of pasta with the thumb and index finger of one hand. The coef of friction between his fingers and the wrapping is 0.3. What horizontal force must he exert to prevent the packet from slipping?

2sin30*0.3 ( angle betweenfingers and wrapping) not sure help me out

The gravity pulls on the packet with a force equal to

F = mg => F = 2*10 = 20 N

The friction needs to be as large as the gravitational force, so that the packet won't move anywhere. The force by the friction is proportional to the normal force by the factor of coef of friction. That we have

F = μN <=> N = F/μ => N = 20/0.3 ≈ 67 N or with correct significant figures 0.07 kN.
• Nov 2nd 2012, 05:37 AM
mysur
Re: Friction problem
Thank you very mcuh for the detail explanation and your time.
• Nov 2nd 2012, 06:52 AM
mysur
Re: Friction problem
But the answer given is 32.7N , p,ease help me out
• Dec 3rd 2012, 12:15 AM
puresoul
Re: Friction problem
You have 2 normal contact forces so the frictional force will be directly proportional to 2N

F=0.3(2N) => N= 20/0.6 => N= 33.3 NAttachment 26031