physics HW question: magnitude of the normal force (A 32.7 kg crate rests on a horizontal floor, and a 77.3 kg person is standing on the crate.)

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Amelinator

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A 32.7 kg crate rests on a horizontal floor, and a 77.3 kg person is standing on the crate. Determine the magnitude of the normal force that the floor exerts on the crate.

I've started this question a couple of times and I'm not sure if the mass of the crate and the person should count as one mass or if the mass of the person should be another force acting on the crate.
 
Amelinator said:
A 32.7 kg crate rests on a horizontal floor, and a 77.3 kg person is standing on the crate. Determine the magnitude of the normal force that the floor exerts on the crate.

I've started this question a couple of times and I'm not sure if the mass of the crate and the person should count as one mass or if the mass of the person should be another force acting on the crate.
Click to expand...
Don't worry about whether to distinguish the forces caused by the person and the crate. How hard does the floor have to push up on the crate?
 
Amelinator said:
A 32.7 kg crate rests on a horizontal floor, and a 77.3 kg person is standing on the crate. Determine the magnitude of the normal force that the floor exerts on the crate.

I've started this question a couple of times and I'm not sure if the mass of the crate and the person should count as one mass or if the mass of the person should be another force acting on the crate.
Click to expand...
The combined mass of the crate and the person standing on it is: 110 kg. (A nice round figure don't you think?)

That (combined) mass resting on the (horizontal) floor will create a (vertically) downward force on the floor as a result of the gravitational field it sits within.

I presume you've been told to use the acceleration due to gravity to be either 10 ms-2 or 9.81 ms-2 and that you know that Force = Mass × Acceleration (P = ma)?

That's all you need to be concerned about for this question (as you've presented it).

Re: "I'm not sure if the mass of the crate and the person should count as one mass or if the mass of the person should be another force acting on the crate."
Actually, it might be a useful exercise for you to calculate the normal reaction both ways and compare your results! 😉

Hope that helps. 😊
 
Last edited:
Amelinator said:
A 32.7 kg crate rests on a horizontal floor, and a 77.3 kg person is standing on the crate. Determine the magnitude of the normal force that the floor exerts on the crate.

I've started this question a couple of times and I'm not sure if the mass of the crate and the person should count as one mass or if the mass of the person should be another force acting on the crate.
Click to expand...
It will be instructive, if you could show following 3 Free Body Diagrams(FBDs) - idealize the man as a crate (box)

(1) FBD of the box with the man standing on top (box on top of a box).

(2) FBD of the the man standing (box ).

(3) FBD of the bottom crate (box).
 
The Highlander said:
The combined mass of the crate and the person standing on it is: 110 kg. (A nice round figure don't you think?)

That (combined) mass resting on the (horizontal) floor will create a (vertically) downward force on the floor as a result of the gravitational field it sits within.

I presume you've been told to use the acceleration due to gravity to be either 10 ms-2 or 9.81 ms-2 and that you know that Force = Mass × Acceleration (P = ma)?

That's all you need to be concerned about for this question (as you've presented it).

Re: "I'm not sure if the mass of the crate and the person should count as one mass or if the mass of the person should be another force acting on the crate."
Actually, it might be a useful exercise for you to calculate the normal reaction both ways and compare your results! 😉

Hope that helps. 😊
Click to expand...
Thank you! This helped a lot!
 
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