Physics Question

[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

The equation to solve these by the way is:

PE = mgh = MASS x GRAVITY x HEIGHT

 

[PowerMac4Ever]

Do your own homework, Romeo

 

[AgaBoogaBoo]

I guess I'm not ahead of you after all

 

[Atomicus]

work = force x distance

so work is just the absolute of the potential energy

 

[neonerd]

Originally posted by: AgaBoogaBoo
I guess I'm not ahead of you after all

Thanks for the free bump :heart:

 

[FoBoT]

where is beavis and butthead when you need them

 

[AgaBoogaBoo]

Originally posted by: neonerd

Originally posted by: AgaBoogaBoo
I guess I'm not ahead of you after all

Thanks for the free bump :heart:

A very kind AT'er bumped before me actually

 

[neonerd]

Originally posted by: AgaBoogaBoo

Originally posted by: neonerd

Originally posted by: AgaBoogaBoo
I guess I'm not ahead of you after all

Thanks for the free bump :heart:

A very kind AT'er bumped before me actually

damn you, i thought i was quoting PowerMac4Ever :|

 

[neonerd]

Originally posted by: Atomicus
work = force x distance

so work is just the absolute of the potential energy

I know in previous equations W = KE

in this problem W = PE?

 

[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

Thanks for the free bump :heart:

A very kind AT'er bumped before me actually

damn you, i thought i was quoting PowerMac4Ever :|

Very smooth :thumbsup:... just like with the ladies!

 

[Evadman]

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

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?

 

[neonerd]

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

Thanks for the free bump :heart:

A very kind AT'er bumped before me actually

damn you, i thought i was quoting PowerMac4Ever :|

Very smooth :thumbsup:... just like with the ladies!

that would explain it, wouldn't it?

 

[neonerd]

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?

 

[MSCoder610]

(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:

 

[TuxDave]

It's equal to A?