Which force best represents Fg?
a)A weight lifter is pushing a barbell upward with a force of 90 N.
b)The weight of a barbell acting on a weight lifter is 80 N.
c)The amount of upward force of a table on a box is 25 N.
d)A box on a rough table has difficulty sliding past 25 N of force.
The Correct Answer and Explanation is:
The correct answer is b) The weight of a barbell acting on a weight lifter is 80 N.
Explanation:
The force labeled as ( F_g ) refers to the gravitational force acting on an object, commonly known as weight. This force is determined by the mass of the object and the acceleration due to gravity. The formula to calculate gravitational force is:
[
F_g = m \cdot g
]
Where:
- ( F_g ) is the gravitational force (or weight),
- ( m ) is the mass of the object,
- ( g ) is the acceleration due to gravity, approximately ( 9.8 \, \text{m/s}^2 ) on Earth.
Gravitational force always acts downward toward the center of the Earth. In this context, the barbell experiences a gravitational pull, which creates a downward force on the lifter. This is the force that the weight lifter must counteract in order to lift the barbell. In answer choice (b), the weight of the barbell is specified as 80 N, which directly represents ( F_g ), the gravitational force acting on the object (barbell) due to its mass and gravity.
Why the other choices are incorrect:
- a) A weight lifter is pushing a barbell upward with a force of 90 N.
This choice describes the force applied by the weight lifter to push the barbell upward. This force is not the gravitational force, but rather an external force exerted to overcome ( F_g ) and move the object upward. - c) The amount of upward force of a table on a box is 25 N.
This is the normal force. The normal force is the upward force exerted by a surface to support the weight of an object resting on it. It balances the object’s weight in many situations but is not the same as the gravitational force acting on the object. - d) A box on a rough table has difficulty sliding past 25 N of force.
This choice refers to the frictional force resisting the motion of the box across the table. Friction is not the same as gravitational force and depends on the texture of the surfaces and the weight of the object.
Therefore, the force described in option b is the correct representation of ( F_g ), the gravitational force acting on the barbell.