A girl is sitting in a sled sliding horizontally along some snow (there is friction present).

The normal force supporting the girl and sled is 636 N.

If the coefficient of static friction is 0.38, and the coefficient of kinetic friction between snow and sled is 0.25, what is the force of friction exerted on the sled?

159 N

Explanation:

There are two types of force of friction:

- Static friction: this is the force of friction that occurs when the object is at rest

- Kinetic friction: this is the force of friction that occurs when the object is in motion

In this problem, the girl is sitting on the sled, and the sled is sliding: this means that the object is in motion, therefore the force of friction that we have to calculate in this problem is the force of kinetic friction.

The force of kinetic friction acting on an object sliding over a flat surface is given by

where

is the coefficient of kinetic friction

N is the normal force on the object

In this problem:

N = 636 N

Therefore, the force of kinetic friction is

atomic = no of protons.

mass number-atomic number = neutron number