A woman pushes a refrigerator across the floor at a steady speed of 20cm/s . If she has to push with a horizontal force of 400 N to keep it moving , is the force of friction less than 400 N , 400 N, more than 400 N, why
For zero acceleration, the net force must be zero. What does that tell you about the friction force?
The force of friction is zero?
constant velocity means NET force of zero.
That means the push exactly balances friction
so friction force is -400 if F is +400
To determine whether the force of friction is less than, equal to, or greater than 400 N, we need to consider Newton's first law of motion, also known as the law of inertia. According to this law, an object at rest will remain at rest, and an object in motion will remain in motion at a constant velocity, unless acted upon by an external force.
In this case, the refrigerator is moving at a steady speed of 20 cm/s, meaning there are no acceleration or deceleration forces acting on it. Therefore, the net force acting on the refrigerator must be zero, as there is no change in its velocity. The force pushing the refrigerator forward is 400 N, and if the refrigerator is moving at a constant speed, the force of friction acting in the opposite direction must also be 400 N. This is because the force of friction opposes the motion of the refrigerator.
So, the force of friction is equal to 400 N.