Work on object lifted in a gravational field

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The discussion revolves around calculating the work done by gravity and by a hand when lifting a book from a table to a shelf. The correct height difference for the work done by gravity is noted as 1.37 m (2.17 m - 0.80 m), leading to a negative work value. Additionally, a separate problem involves calculating the net work required to change the velocity of a 10 g particle, with initial calculations yielding an incorrect result of 1.7. Ultimately, the participant realizes their mistake and decides to abandon the second question. The thread highlights common challenges in applying physics formulas correctly.
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A 1.1 kg book is lying on a 0.80-m-high table. You pick it up and place it on a bookshelf 2.17 m above the floor.

How much work does gravity do on the book?
How much work does your hand do on the book?

W=mgh

(1.1 kg)(9.8 m/s^2)(0.8m)=8.6

The answers that I am getting are wrong
Please help
 
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The book is initially on the table and then its moved to the shelf. So it moved (2.17-0.8) m
Also, work done by gravity will be negative.
 
Help

Now I have another problem

A 10 g particle is moving to the left at 29 m/s. How much net work must be done on the particle to cause it to move to the right at 47 m/s?

W=mg\Deltar

I got 1.7. I don't think I am doing this right.
 
sracks said:
I got 1.7. I don't think I am doing this right.

Show us how you got 1.7 :confused:

(btw, if you type alt-j, it give you ∆ without having to tex! :smile:)
 
(.01kg)(9.8m/s^2)(47 m/s - 29m/s) = 1.7

I have a feeling that i am completely doing it wrong
 
Got it

Forget about this question. I got it
 

Thread 'Errors and significant figures'

I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
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Thread 'A cylinder connected to a hanging mass'

Thread 'A cylinder connected to a hanging mass'

Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
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