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Confused about answer to problem.

  • Thread starter SammyLP250
  • Start date
  • #1
10
0

Homework Statement



A 1.57 kg brick measures 20.0 cm x 8.00 cm x 5.50 cm. Taking the zero of potential energy when the brick lies on its broadest face. (a) What is the potential energy when the brick is standing on end? Note: You can treat the brick as though all its mass is concentrated at its center. (b) What is the potential energy when it's balanced on its 8 cm edge?


Homework Equations



Ug=mgh

The Attempt at a Solution



I could not figure out the first part of the question because I don't know what "standing on end" means.

As for B:

m = 1.57 kg
g = 9.81
h = 0.08 m

Ug = (1.57)(9.81)(0.08) = 1.23 J

That is the answer I get, but Mastering Physics tells me that there was a rounding error and the answer is 1.17 J and I cannot figure out where I was wrong. This is not supposed to be a hard problem. Maybe I'm thinking too hard about it??
 
Last edited:

Answers and Replies

  • #2
1,065
10
Check the difference of CM between 20.0 cm x 8.00 cm surface facing the floor and that of
8.00 cm x 5.50 cm.

I guess it is between the broadest and the least broad. There are 3 dimensions of faces.
 
  • #3
10
0
Thanks for replying! Could you explain to me what you mean by check the difference? I'm a little slow...
 
  • #4
1,065
10
If it is standing with height of 20cm, then the height of CM is 10cm.
Likewise if it is standing with height of 5.5cm, then the CM must be (5.5/2)cm
 

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