Bob is pulling a 30 kg filing cabinet with a force of 200 N, but the filing cabinet refuses to move. The coefficient of static friction between the filing cabinet and the floor is 0.80. What is the magnitude of the friction force on the filing cabinet?

Video transcript

Hi, everyone in this practice problem, we're being asked to determine the force of friction acting on a refrigerator. We will have Mike who is working as a helper in an appliance showroom, who is trying to pull a 25 kg refrigerator with a force of 125 Newton. Mike will not be able to move it. And we're being asked to determine the force of friction acting on the refrigerator. If the coefficient of static friction between the refrigerator and the showroom floor is 0.6. The options given for the force of frictions are a 147 Newton B 125 Newton C 245 Newton and the 120 Newton. So we will consider the refrigerator as a particle and the pictorial representation of the system. In the problem statement will be given by this pictorial representation or this free body diagram right here. So this square is going to represent our refrigerator, although it is going to be a particle. And it is given in the problem statement that Mike is going to pull the refrigerator with a force of F equals 125 Newton. However, the refrigerator will not uh move and it will experience a friction or force of friction, which will be represented here by our, a blue arrow of F S because it is still static, the refrigerator is not moving. Hence, it is going to be at equilibrium. So not moving will means that it is at equilibrium. So because of uh because it is at equilibrium, then the net force acting on the refrigerator or Sigma F will equals to zero. This is going to be based on the Newton's law where when a system is at equilibrium, the Sigma net force acting on the system is going to equals to zero. So the frictional force in this case will have the same exact value as the force applied by a mic to pull the refrigerator because the only two forces acting on the refrigerator. In this case, in the horizontal axis or in the X axis here is going to just be the force or the pulling force and the static friction force. So in this case, Sigma FX will equals to zero and Sigma FX will equals to F minus F S equals to zero. So F S will equals to F which will equals to 125 Newton. So the static force of friction experienced by the refrigerator is going to be 125 Newton which will correspond to option B in our answer choices. So option B will be the answer to this particular practice problem and that'll be it for this video. If you guys still have any sort of confusion, please make sure to check out our other lesson videos on similar topics and that'll be it for this one. Thank you.