An 8.0-kg object rests on the floor of an elevator which is accelerating downward at a rate of 1.3 m/s2. What is the magnitude of the force the object exerts on the floor of the elevator?
A)59 N
B)10 N
C)89 N
D)68 N
E)78 N

Question

Quizplus · Accepted Answer

The force exerted by the object on the elevator floor is equal in magnitude and opposite in direction to the force exerted by the elevator floor on the object (Newton's third law). 
Using Newton's second law, F = ma, where F is the net force acting on the object, m is the mass of the object, and a is the acceleration of the object.
In this case, the net force acting on the object is the force exerted by the elevator floor on the object, which is the unknown we are trying to find. The mass of the object is 8.0 kg, and the acceleration of the object is the same as the acceleration of the elevator, which is -1.3 m/s^2 (negative because it is accelerating downward).
Plugging these values into the equation F = ma, we get F = (8.0 kg)(-1.3 m/s^2) = -10.4 N.
Since the force is downward (opposite to the upward force of gravity), we take the magnitude of the force as positive, giving us a final answer of 10.4 N, which is closest to 10 N (choice D).

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