A physics professor lifts her 9.0-kg briefcase at constant speed with an upward force. Find the magnitude of her force.
To find the magnitude of the force the physics professor applies to lift her briefcase, we can use Newton's second law of motion, which states that the net force acting on an object is equal to the mass of the object multiplied by its acceleration.
In this case, the briefcase is being lifted at a constant speed, which means it has zero acceleration. According to Newton's second law, if an object has zero acceleration, the net force acting on it is also zero. However, we also know that the professor is applying an upward force to lift the briefcase.
In this situation, there are two forces acting on the briefcase: the gravitational force pulling it downward and the professor's upward force counteracting the gravitational force. These two forces must cancel each other out for the briefcase to remain at constant speed. Therefore, the magnitude of the professor's upward force must be equal in magnitude but opposite in direction to the gravitational force.
The gravitational force acting on the briefcase can be calculated using the equation F = mg, where F is the force, m is the mass, and g is the acceleration due to gravity, which is approximately 9.8 m/s² on Earth.
Substituting the given values, the gravitational force on the briefcase is:
F = (9.0 kg) * (9.8 m/s²) ≈ 88.2 N
Since the magnitude of the professor's upward force must be equal to the gravitational force, the magnitude of her force is also approximately 88.2 N.