Calculating Friction Force on a Resting Block

[physaru86]

A 1.2 kg block is resting on horizontal surface. The coefficient of static friction between block and
surface is 0.5. What is the magnitude and direction of force of friction on block when magnitude of external force acting of block in the horizontal direction is 9.8 N f_s = μ_s*N, N = mg

m = 1.2 kg, μ_s = 0.5, g = 9.8
f_s = 0.5*1.2*9.8 N = 5.88 N

 

[Chestermiller]

Is this really the full problem statement, exactly as presented, because something seems wrong about it.

Chet

 

[physaru86]

Is this really the full problem statement, exactly as presented, because something seems wrong about it.

Chet

please tell me what is wrong about it?

 

[Chestermiller]

If the applied force is less than the normal force times the coefficient of static friction, then the friction force will equal the applied force and the body will not move. If the applied force is equal to the normal force times the coefficient of static friction, then the friction force will equal the applied force and the body will be on the verge of moving. But, in your example, the applied force is greater than the normal force times the coefficient of static friction, so the body will move, and kinetic friction will prevail; in this case, the coefficient of static friction is irrelevant, as is the normal force times the coefficient of static friction.

Chet

 

[physaru86]

S

If the applied force is less than the normal force times the coefficient of static friction, then the friction force will equal the applied force and the body will not move. If the applied force is equal to the normal force times the coefficient of static friction, then the friction force will equal the applied force and the body will be on the verge of moving. But, in your example, the applied force is greater than the normal force times the coefficient of static friction, so the body will move, and kinetic friction will prevail; in this case, the coefficient of static friction is irrelevant, as is the normal force times the coefficient of static friction.

Chet

So can the force of kinetic friction be found? if so how to find

 

[Chestermiller]

S

So can the force of kinetic friction be found? if so how to find

To find that, you need to know the coefficient of kinetic friction.

Chet

 

[physaru86]

To find that, you need to know the coefficient of kinetic friction.

Chet

Yes it was the same doubt i had. can the coefficient of kinetic friction be found

 

[Chestermiller]

Yes it was the same doubt i had. can the coefficient of kinetic friction be found

Sure, it can be measured.

Chet

 

[physaru86]

Sure, it can be measured.

Chet

thanks

 

[joaopedro._]

Oposed to motion