Quiz Revisions: Bored during the Pandemic, you decided that this would be the perfect time to redesign your
kitchen AND practice physics. So you push your fridge. Your fridge has a mass of 150 kg and
the coefficient of kinetic friction between your fridge
and the ground is.35. You
push the fridge
with a force of 600 N. You push the fridge a distance of 5 m.
1. What is the frictional force the fridge experiences?
Student Response: The fridge experiences a frictional force of .35.
Why is this student incorrect? What should the answer be?

fr = 514.5 N,    This force has the opposite direction to the applied force.

Explanation:

Let's propose the solution of the problem using Newton's Second Law, we place a reference frame with the horizontal x-axis

Y axis

         N- W = 0

         N = W

X axis

         F -fr = m a

the friction force has the expression

        fr = μ N

        fr = μ mg

        fr = 0.35  150  9.8

        fr = 514.5 N

This force has the opposite direction to the applied force.

The student's answer is incorrect because the friction coefficient must be multiplied by the normal

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.

if the person is shown to have +90n, then ans is -10n.

if the person is shown to have -90n, then ans is +10n.