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

1. Dec 17, 2012

### HelloImAsh

1. The problem statement, all variables and given/known data
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?

2. Relevant 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

3. 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
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Dec 17, 2012

### lewando

400kg? The force due to friction is based on the mass of the sled. Not sled + dogs.

3. Dec 17, 2012

### Apollinaria

Tried it that way. Doesn't work out right either.

4. Dec 17, 2012

### lewando

Typo? (250kg*9.8m/s2*0.16)/5 = 78.4N

5. Dec 18, 2012

### CWatters

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.