How Is Acceleration Calculated When a Bureau Starts Moving on a Rough Surface?

[grouchy]

Homework Statement

A bureau rests on a rough horizontal surface ( mk=0.40, ms=0.50). A constant horizontal force, just sufficient to start the bureau in motion, is then applied.The acceleration of the bureau is:

Homework Equations

F= ma

The Attempt at a Solution

The answer is 0.98 m/s^2 but I'm not sure why. I thought you would only use the kenetic friction since it just starts to move.

 

[Dick]

You use the static friction to get the applied force. Once it's moving the applied force doesn't change, but now use kinetic friction in your force balance.

 

[pinkyjoshi65]

how can you get the applied force using the coefficient of static friction?..Coefficient of static friction= Fs/Fn

 

[Dick]

how can you get the applied force using the coefficient of static friction?..Coefficient of static friction= Fs/Fn

Fn=mg. Fs=0.5*mg. To start it moving the applied force must be equal to Fs.

 

[pinkyjoshi65]

ohk..I see..so grouchy's answer is right, although the method is not

 

[Dick]

ohk..I see..so grouchy's answer is right, although the method is not

He didn't have a method. Hopefully now he does.

 

[grouchy]

ok, so you take the fs and subtract the fk? right?

 

[Dick]

Why the question marks? fs is the force pushing the cabinet - fk is the force acting against the push. Use the total force on the cabinet to compute it's acceleration.