When a 100-N force acts horizontally on an 8.0-kg chair, the chair moves at a constant speed across the level floor. Which statement has to be true? The chair accelerates at 12.5 m/s^2
The applied force is greater than the frictional force.
The friction force is 100 N
There is no friction between the floor and chair

The applied force is greater than the frictional force.

Explanation:

the chair moves at a constant speed therefore, the answer is not A or C.

if there is no friction then the chair would accelerate and it would not be at a constant speed.

hence, the only possible answer is B.

conduction, convection, radiation

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.