Friction Q: box of mass 150 kg stands on horizontal surface

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christou1990

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hi, im having trouble with this question, any possible help would be very niceee, thanks.

A box of mass 150 kg stands on a horizontal surface.
(a) If the coefficient of static friction between the box and the surface is 0.45, what is the force required just to start the sliding?
(b) If the force required to keep the box moving is 400N, what is the coefficient of dynamic friction between the box and the surface?
(c) In emergency situations a patient with major blood loss is placed in a position in which the foot of the bed is raised to get maximum blood flow to the brain (in the head). If the coefficient of static friction between the patient and the bed is 0.8, what is the maximum angle to the horizontal that the bed can be raised before the patient begins to slide?
 
christou1990 said:
hi, im having trouble with this question, any possible help would be very niceee, thanks.


A box of mass 150 kg stands on a horizontal surface.
(a) If the coefficient of static friction between the box and the surface is 0.45, what is the force required just to start the sliding?
Hint:
Draw the free-body-diagram (FBD) first showing all the forces acting at equilibrium

Apply Newtons law [sub:5fok6ih9]\(\displaystyle \sum {F} \, = \, 0\)[/sub:5fok6ih9]
(b) If the force required to keep the box moving is 400N, what is the coefficient of dynamic friction between the box and the surface?

Same as above

(c) In emergency situations a patient with major blood loss is placed in a position in which the foot of the bed is raised to get maximum blood flow to the brain (in the head). If the coefficient of static friction between the patient and the bed is 0.8, what is the maximum angle to the horizontal that the bed can be raised before the patient begins to slide?

Same as above
Click to expand...
Please show us your work, indicating exactly where you are stuck, so that we know where to begin to help you.
 
A box of mass 150 kg stands on a horizontal surface.
(a) If the coefficient of static friction between the box and the surface is 0.45, what is the force required just to start the sliding?
(b) If the force required to keep the box moving is 400N, what is the coefficient of dynamic friction between the box and the surface?
(c) In emergency situations a patient with major blood loss is placed in a position in which the foot of the bed is raised to get maximum blood flow to the brain (in the head). If the coefficient of static friction between the patient and the bed is 0.8, what is the maximum angle to the horizontal that the bed can be raised before the patient begins to slide?
Click to expand...

For a) and b):

Frictional force, F = mu (coefficient of friction) x N (normal force)

On a horizontal surface, N = W (weight) if no other vertical forces are applied.

W = mg (mass x acceleration due to gravity)

Putting the pieces together

F = (mu)(mg)

Hope that helps.
 
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