• We’re currently investigating an issue related to the forum theme and styling that is impacting page layout and visual formatting. The problem has been identified, and we are actively working on a resolution. There is no impact to user data or functionality, this is strictly a front-end display issue. We’ll post an update once the fix has been deployed. Thanks for your patience while we get this sorted.

Physics Question

N

neonerd

Diamond Member
In starting and exercise, a 1.60-m tall person lifts a 2.10-kg book on the ground so it is 2.20 m above the ground. What is the potential energy of the book relative to (a) the ground, (b) the top of the person's head? (c) How is the work done by the person related to the answers in parts (a) and (b)?

For (a) i got an answer of 45.28-J
For (b) i got an answer of 12.35-J

I don't understand what (c) is asking 😕

The equation to solve these by the way is:

PE = mgh = MASS x GRAVITY x HEIGHT
 
Originally posted by: neonerd
In starting and exercise, a 1.60-m tall person lifts a 2.10-kg book on the ground so it is 2.20 m above the ground. What is the potential energy of the book relative to (a) the ground, (b) the top of the person's head? (c) How is the work done by the person related to the answers in parts (a) and (b)?

For (a) i got an answer of 45.28-J
For (b) i got an answer of 12.35-J

I don't understand what (c) is asking 😕
Click to expand...
C means if the lifter dropped the book, his head would have to absorb 12.35 Joules. The real questions should be, how many Joules are expended in producing sound and heat when the book smaches into the lifters head, and how much energy must the person's head dissipate?

 
Originally posted by: PowerMac4Ever
Originally posted by: neonerd
Originally posted by: AgaBoogaBoo
Originally posted by: neonerd
Originally posted by: AgaBoogaBoo
I guess I'm not ahead of you after all 😛
Click to expand...

Thanks for the free bump :heart:
Click to expand...

A very kind AT'er bumped before me actually
Click to expand...

damn you, i thought i was quoting PowerMac4Ever :|
Click to expand...
Very smooth :thumbsup:... just like with the ladies!
Click to expand...

that would explain it, wouldn't it? 😛
 
wait, so does it just mean that if gravity has a PE of 45.28, then the work the person is going is -45.28-J?
 
(C) means, assuming all of the work the person does goes directly into lifting the book, that the person did (a) joules of work to lift it from the floor to 2.20m above the floor, and (b) joules of work to lift the book from the height of his head to 2.20m.

KEi + PEi + Wext = KEf + PEf. If there's no change in kinetic energy, the work is the change in (gravitational) potential energy.

Assuming I understood the problem, anyway :thumbsup:
 
You must log in or register to reply here.

TRENDING THREADS

Back
Top