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

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Homework Help Overview

The problem involves calculating the applied force required by dogs to pull a sled at a constant velocity, given the mass of the sled and the coefficient of kinetic friction. The context is centered around forces, friction, and motion in a horizontal plane.

Discussion Character

  • Conceptual clarification, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to calculate the force of friction using the combined mass of the sled and dogs, leading to a discrepancy with the expected answer. Some participants question the mass used in the calculations, suggesting it should only be the sled's mass. Others propose alternative calculations and express confusion over potential typos in the problem statement.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the problem setup and calculations. Some have provided alternative calculations that yield different results, indicating a productive examination of the assumptions involved.

Contextual Notes

Participants are working under the assumption that the sled's mass is 250kg, but there is uncertainty regarding the correct mass to use for the friction calculation. The coefficient of kinetic friction is also a point of discussion, as different values have been mentioned.

HelloImAsh
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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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