Asled with a mass of 20 kg slides along frictionless ice at 4.5 m/s. it then crosses a rough patch of snow that exerts a friction force of 12 n. how far does it slide on the snow before coming to rest?

Use Newton's second law to determine the acceleration being applied to the sled. There are three forces at work on the sled (its weight, the force normal to the ground, and friction) but two of them cancel, leaving friction as the only effective force. This vector is pointed in the opposite direction of the sled's movement, so if we take the direction of its movement to be the positive axis, we would find the acceleration due to the friction to be

Now we use the formula

to find the distance it travels. The sled comes to a rest, so , and let's take the starting position to be the origin. Then the distance traveled is