Question

If you pull a resistant puppy with its leash in a horizontal direction, it takes 80 N to get it going. You can then keep it moving at constant speed across the floor with a constant, horizontal force of 70 N. The puppy has a weight of 110 N. What is the coefficient of static friction between the puppy and the floor

Answer 1

Answer:

The coefficient of static friction between the puppy and the floor is 0.7273.

Explanation:

The horizontal force applied to move the puppy from a steady state has to be greater than the force of static friction, after it is moving the force needs to be equal to be greater than the force of dynamic friction in order to maintain its movement. The force of static friction is given by:

$F_s = \mu_s*N$

Where $F_s$ is the static friction force, $\mu_s$ is the coefficient of static friction and $N$ is the normal force. Since there's no angle on the flor the normal force is equal to the weight of the puppy, therefore, $N = 110\text{ N}$, to make the puppy moving we need to use a force of 80 N, therefore, $F_s = 80 \text{ N}$, so we can solve for the coefficient as shown below:

$80 = \mu_s*110\\\mu_s = \frac{80}{110} = 0.7273$

The coefficient of static friction between the puppy and the floor is 0.7273.