What force does the water exert on the man?

A question on frictional force?

• A 35 kg crate is at rest on the floor. A man attempts to push it across the floor by applying a 100 N force horizontally. (a) Take the coefficient of static friction between the crate and floor to be 0.37 and show that the crate does not move. (b) A second man helps by pulling up on the crate. Calculate the minimum vertical force he must apply so that the crate starts to move across the floor. (c) If the second man applies a horizontal rather than a vertical force, what minimum force, in addition to the 100 N force of the first man, must he exert to get the crate started? I saw the solution to subquestion (b), and the solution implies that if the frictional force is equals to the force applied, the crate will start to move, but isn't it by convention that if the applied force is still equals to the static friction, the object will not move? The solution for subquestion (b) is: For the box to move, Frictional force = Applied Force = 100N Fn = Frictional force/coefficient of static friction = 100/0.37 = 270N The current normal force = 343N So in order for the crate to move, the second man has to lift the crate with a force of (343-270)N = 73N

• Answer:

  U seem to be asking about sol'n (b) so I will just discuss that part: When the MAX STATIC friction force = the force applied, there exists what is called STATIC EQUILIBRIUM. Under equilibrium an additional force, of *any* size is able to move the object. So if U want to say that a force of 100.00000000000000000000000000000001 N is required to move object, OK, but then someone else could add another decimal 0 etc, etc ...so why not allow 100 N to be the size of the force that moves the object - it's close enough, no? :>)