Consult to explore a model for solving this problem. A person pushes on a 55-kg

Question

Consult   to explore a model for solving this problem. A person pushes on a 55-kg refrigerator with a horizontal force of -280 N; the minus sign indicates that the force points in the -x direction. The coefficient of static friction is 0.60. (a) If the refrigerator does not move, what are the magnitude and direction of the static frictional force that the floor exerts on the refrigerator? (b) What is the magnitude of the largest pushing force that can be applied to the refrigerator before it just begins to move? Assume g = 9.8 m/s2.

Explanation / Answer

(a) Since the only forces in the horizontal direction are F, theapplied force and f, the frictional force,

for the refrigerator to be static,

F - f = 0

So, f = 280 N

Also, its direction is opposite to applied force , ie. +x direction.

b)

For the refrigerator to begin moving,

the applied force, F must be greater than the maximumlimiting force of static friction between the refrigerator and the floor.

fmax = ?*N, where fmax = limiting static frictionalforce,

? = coefficient of static friction between the refrigeratorand the floor

N = normal reaction between the floor and the refrigerator

In the vertical direction,

for static condition,

N = W = weight of the refrigerator = 55*9.80 N = 539 N

in the +y direction.

Now, fmax = F = ?*N = 0.60*539 N = 323.4 N

If you apply any force less than this value, the refrigeratorwouldn't move.

So, the answer to (b) is 323.4 N

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