How to find applied force when given force of friction (constant velocity)

AI Thread Summary
To find the applied force needed for five dogs to pull a 250kg sled at constant velocity, the force of kinetic friction must be calculated using the coefficient of kinetic friction (0.14) and the sled's mass. The correct calculation shows that the force of friction is 250kg multiplied by 9.8m/s² and then by 0.14, resulting in a total friction force of 343N. Dividing this by five dogs indicates each dog must exert approximately 68.7N to maintain constant velocity. There appears to be confusion regarding the mass used in calculations, as some participants mistakenly included the mass of the dogs. The final consensus suggests a reevaluation of the problem statement for potential errors.
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Homework Statement


Five dogs, each having a mass of 30kg, pull a 250kg sled horizontally across the snow (coefficient of kinetic friction = 0.14).
How much force must each dog exert in order to move the sled at a constant velocity?

Homework Equations


Force of kinetic friction = coefficient of kinetic friction*normal force
Rewritten, the equation above would be F{k}=μ*F{n}
Also, normal force = gravitational force = mass*gravity

The Attempt at a Solution


F{k}=μ*F{n}
=0.14*m*g
=0.14*400kg*9.8N/kg
=549N
Therefore each dog would have to pull with 549/5=110N of force in order for the sled to move at constant velocity.

The problem is, in my workbook it shows that the answer should be 78.4N. What am I doing wrong?
Thanks :smile:
 
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400kg? The force due to friction is based on the mass of the sled. Not sled + dogs.
 
lewando said:
400kg? The force due to friction is based on the mass of the sled. Not sled + dogs.

Tried it that way. Doesn't work out right either.
 
Typo? (250kg*9.8m/s2*0.16)/5 = 78.4N
 
I agree with lewando.

If the problem statement is correct then answer should be..

250kg*9.8m/s2*0.14/5 = 68.7N

Has to be a typo somewhere.
 
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