Final answer:
The scale exerts a normal force of 150 pounds on Brad, which is equal to the force he exerts on the scale. Bathroom scales measure this force but are calibrated to display mass. The scale reading varies with acceleration, such as in an elevator.
Step-by-step explanation:
The force that the scale exerts on Brad is known as the normal force. This force is equal and opposite to the force Brad exerts on the scale due to Newton's Third Law of Motion, which states that for every action, there is an equal and opposite reaction. Since Brad is exerting a downward force of 150 pounds, the scale must exert an upward normal force of 150 pounds to support him, assuming he is not accelerating (which would be the case if he is stationary or moving at constant velocity).
Bathroom scales measure this normal force to provide a reading of weight. However, the reading in pounds can be misleading because it is actually a measure of force, not mass. In most countries, bathroom scales are calibrated to display mass in kilograms, dividing the weight measurement by 9.80 m/s2 to convert from newtons to kilograms.
If Brad were to use the scale in an elevator, the reading could vary depending on the elevator's motion. If the elevator accelerates upwards, the scale would read a value greater than his actual weight. When moving at a constant speed or standing still, the scale would show his actual weight because there is no acceleration.
Similarly, if Brad were standing on the scale and exerting a force on a table next to him, the reading on the scale might change. The correct answer to what happens if Brad pushes down on a table while standing on a scale is option b, because the scale would read less, not more, since part of Brad's weight is being supported by the table.