Question

Please help!
A 1.5 kg book falls 1.12 m from a table to the
floor.
(a) How much work did the gravitational force
do on it?
Answer: Gravitational potential energy = mgh
= 1.5(9.81)(1.12) = 16 J [2 sig figs]

Is this okay?

(b) How much gravitational potential energy
did it lose?

- I don't know how to answer this question.

Answer 1

a) work = force x distance... you have the rest there, write your answer and I'll tell you if you're right

b)PE = mass x gravity x height
PE before fall - PE after fall = loss of PE
as height after fall = 0 (relatively), just work out PE before fall for your answer

Answer 2

is my answer for (a) wrong then? i used the GPE formula to find the energy for work done as they have the same SI unit.

Answer 3

what you worked out for a before was the potential energy, not the work done.
use that equation for b and you'll be on track though

Answer 4

I know that work = force x distance but i don't have the force or acceleration that can help me find the force exerted.

Answer 5

damn, gravity is an acceleration, not a force, yep, your completely correct for a, my bad

Answer 6

thank you =)

Answer 7

so what about b? =)

Answer 8

work done = delta energy = change in PE in this case
so i think your answer should be the same once it come to a rest on the ground...

Answer 9

i didn't understand your expla?

Answer 10

*explanation because i'm confused about the fact that GPE is affect by the acceleration due to gravity.

Answer 11

so, shouldn't the answer for b supposed to be the same as part a?

Answer 12

PE = mass x gravity x height
PE before fall - PE after fall = loss of PE
as height after fall = 0 (relatively)
so the Potential Energy is the energy it would give up in an ideal environment in going from that height to a lower height

both work done on an object and energy are measured in Joules

Answer 13

yep, b should equal a

Answer 14

That really helped. Thank you.

Answer 15

welcome, sorry for the false start

Answer 16

they are equal but a should be -16

Answer 17

it's no biggie.

Answer 18

@lalaly actually B should equal -16J, but as the question is posed as "what is the LOSS of PE", i think it's safe to answer both with positive intergers