Net Force of 60 kg Person in Elevator: Up/Down

[barthayn]

Homework Statement

What is the net force of a 60 kg person, in Newtons, in an elevator accelerating at 5 m/s/s;
a) upwards?
b) downwards?

Homework Equations

F = ma

The Attempt at a Solution

a) F = 60 (5+9.8)
F = 60 * 14.8
F = 888 N [up]

b) F = 60 (-5+9.8)
F = 60 * 4.8
F = 288 N


Are my answers correct? If they are it is because you have to use vectors and do the change in acceleration to get the acceleration correct?

 

[Apphysicist]

Net force on the person or the normal force on the person by the elevator?

 

[barthayn]

Net force on the person or the normal force on the person by the elevator?

Net force on the person. The normal force would just be mass multiplied by the acceleration due to gravity correct?

 

[Apphysicist]

Net force on the person. The normal force would just be mass multiplied by the acceleration due to gravity correct?

Actually no. If you consider that the forces on the person are just the normal force of the elevator on the person and the gravitational force, in order to have a net acceleration of 5m/s² of both the person and elevator, your normal force has to exceed the gravitational force.

At least that's how I read the problem. I see elevator problems and they usually ask for the normal force, since given a net acceleration and gravitational force, the normal force is what is unknown.

 

[barthayn]

So is my answers for the net force of the person correct? Which are:

a) F = 60 (5+9.8)
F = 60 * 14.8
F = 888 N [up]

b) F = 60 (-5+9.8)
F = 60 * 4.8
F = 288 N [down]