Respuesta :
Answer:
a) 70 N, b) b. Each initially applied a force bigger than static friction to get the box moving and accelerating, then when the desired final speed was achieved they reduced the force to make the net force zero.
Explanation:
a) A constant speed means that magnitude of friction force is equal to the magnitude of the external force. The friction force is directly proportional to the normal force, which is equal to the weight of the box. Therefore, the magnitude of the force is 70 N.
b) Alice used initially a greater force to accelerate the box up to needed speed and later reduced the external force to keep speed constant. The right choice is option b.
(a) The magnitude of the force that Alice is applying to the box is 70 N.
(b) Each initially applied a force bigger than static friction to get the box moving and accelerating, then when the desired final speed was achieved they reduced the force to make the net force zero.
Force applied by Alice
Constant speed means zero acceleration and the magnitude of friction force is equal to the magnitude of the external force.
F - Ff = 0
F = Ff
The friction force is directly proportional to the normal force, which is equal to the weight of the box.
Thus, the magnitude of the force that Alice is applying to the box is 70 N.
Condition for constant speeds
Each initially applied a force bigger than static friction to get the box moving and accelerating, then when the desired final speed was achieved they reduced the force to make the net force zero.
Learn more about static friction here: https://brainly.com/question/13680415