Instructions Click 'start' in the following Active Figure depicting static and kinetic frictional forces with a given applied force to a trash can to complete the exercise. EXPLORE A trash can with a mass of 11 kg has a coefficient of static friction of μg 0.88 and a coefficient of kinetic friction of μ = 0.40. (The Active Figure applies to a similar situation, but the values of the mass, coefficient of static friction and coefficient of kinetic friction may be different. So the values it gives may not be the same values you obtain from your calculations.) (A) What is the maximum horizontal force F that can be exerted without moving the trash can? (B) Suppose this force is just barely exceeded. Determine the acceleration of the trash can as it moves. CONCEPTUALIZE The trash can is being pushed near its base but the applied force is balanced by the force of static friction. The maximum force of static friction is determined by the coefficient of static friction and the normal force that the ground exerts on the trash can. Display in a New Window CATEGORIZE We seek the largest horizontal force F that can be applied without moving the trash can. Examine when it is possible to balance the forces to have no acceleration; this is a problem of balanced forces and equilibrium.

University Physics Volume 1
18th Edition
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Chapter6: Applications Of Newton's Laws
Section: Chapter Questions
Problem 123AP: Two blocks connected by a string are pulled across a horizontal surface by a force applied to one of...
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Instructions Click 'start' in the following Active Figure depicting static and kinetic frictional forces with a given applied
force to a trash can to complete the exercise.
EXPLORE
A trash can with a mass of 11 kg
has a coefficient of static friction
of Ms
= 0.88 and a coefficient of
kinetic friction of μk = 0.40. (The
Active Figure applies to a similar
situation, but the values of the
mass, coefficient of static friction
and coefficient of kinetic friction
may be different. So the values it
gives may not be the same
values you obtain from your
calculations.)
(A) What is the maximum
horizontal force F that can be
exerted without moving the trash
can?
(B) Suppose this force is just
barely exceeded. Determine the
acceleration of the trash can as it
moves.
CONCEPTUALIZE
The trash can is being pushed
near its base but the applied
force is balanced by the force of static friction. The maximum force of static friction is determined by the coefficient
of static friction and the normal force that the ground exerts on the trash can.
Display in a New Window
CATEGORIZE
We seek the largest horizontal force F that can be applied without moving the trash can. Examine when it is possible
to balance the forces to have no acceleration; this is a problem of balanced forces and equilibrium.
Transcribed Image Text:Instructions Click 'start' in the following Active Figure depicting static and kinetic frictional forces with a given applied force to a trash can to complete the exercise. EXPLORE A trash can with a mass of 11 kg has a coefficient of static friction of Ms = 0.88 and a coefficient of kinetic friction of μk = 0.40. (The Active Figure applies to a similar situation, but the values of the mass, coefficient of static friction and coefficient of kinetic friction may be different. So the values it gives may not be the same values you obtain from your calculations.) (A) What is the maximum horizontal force F that can be exerted without moving the trash can? (B) Suppose this force is just barely exceeded. Determine the acceleration of the trash can as it moves. CONCEPTUALIZE The trash can is being pushed near its base but the applied force is balanced by the force of static friction. The maximum force of static friction is determined by the coefficient of static friction and the normal force that the ground exerts on the trash can. Display in a New Window CATEGORIZE We seek the largest horizontal force F that can be applied without moving the trash can. Examine when it is possible to balance the forces to have no acceleration; this is a problem of balanced forces and equilibrium.
ANALYZE
(A) What is the maximum horizontal force F that can be exerted without moving the trash can?
The surfaces are extremely rough, and only a fraction of the surfaces is in close contact, but we make the
assumption that the relation between the friction force and normal force applies.
The maximum possible force of static friction is
= μsn
Fs, max
where n is the magnitude of the normal force exerted by one surface on the other. For an applied force that is too
small to move the trash can, the force of static friction balances the applied force and both have the same magnitude
which, because n = mg, is equal to
F = Fs, max = μçmg
where
Ms
is the coefficient of static friction. This gives
F = Fs, max
=
(B) Determine the acceleration of the trash can as it moves.
N.
For a force F that is just slightly larger than Fs, max, the trash can accelerates. The applied force can still be taken as
the same, but the friction force is given by the coefficient of kinetic friction μk times the normal force n instead of the
coefficient of static friction μ times the normal force n:
FK = μkmg.
The net force that gives the mass times the acceleration is the difference of the applied and kinetic friction forces:
μkmg = μsmg - μkmg = (μs - μk)mg
= max.
ΣΕ
= Fs, max
X
This can be solved to give the acceleration:
ax
(Ms - Mk)g=
=
m/s².
FINALIZE
If the applied force is suddenly removed from the moving trash can, the force of kinetic friction continues to act with
no applied force as long as the trash can is moving. Consider how this affects the motion of the trash can.
Transcribed Image Text:ANALYZE (A) What is the maximum horizontal force F that can be exerted without moving the trash can? The surfaces are extremely rough, and only a fraction of the surfaces is in close contact, but we make the assumption that the relation between the friction force and normal force applies. The maximum possible force of static friction is = μsn Fs, max where n is the magnitude of the normal force exerted by one surface on the other. For an applied force that is too small to move the trash can, the force of static friction balances the applied force and both have the same magnitude which, because n = mg, is equal to F = Fs, max = μçmg where Ms is the coefficient of static friction. This gives F = Fs, max = (B) Determine the acceleration of the trash can as it moves. N. For a force F that is just slightly larger than Fs, max, the trash can accelerates. The applied force can still be taken as the same, but the friction force is given by the coefficient of kinetic friction μk times the normal force n instead of the coefficient of static friction μ times the normal force n: FK = μkmg. The net force that gives the mass times the acceleration is the difference of the applied and kinetic friction forces: μkmg = μsmg - μkmg = (μs - μk)mg = max. ΣΕ = Fs, max X This can be solved to give the acceleration: ax (Ms - Mk)g= = m/s². FINALIZE If the applied force is suddenly removed from the moving trash can, the force of kinetic friction continues to act with no applied force as long as the trash can is moving. Consider how this affects the motion of the trash can.
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