# 2 theory related multiple choice questions

hey, I'm currently in grade 12, and so far we just started a review over the conservation laws unit, which includes (energy related theorm, work, power, momentum, collisions, mechanical energy ect.)

Anyways I cant seem to figure out these two multiple choice theory questions, was hoping someone can explain them to me, thanks.

Which statement describes a conclusion that can be made about a closed system where there has been an increase in its enery?
a)Work has been done on the system
b)Mass has been converted to energy
c)Kinetic energy of the system is increased
d)Potential energy of the system has decreased

And: "Ruth" is diving from a tower 10.0m above the water. When she is 5.0m above the surface of the water her:
a)momentum and kinetic energy are about equal
b)velocity is half of the velocity she will have when she touches the water
c)potential energy, with respect to the water, and her momentum are about equal
d)potential energy, with respect to the water, and her kinetic energy about equal
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was hoping someone can explain these theory questions to me, thanks alot.

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Conservation of energy

for the second question:
find the potential energy when she was 5 m above the water.
use the law of conservation of energy to find her kinetic energy 5 m above the water : potential energy at 10 m = potential energy at 5 m + kinetic energy when she was 5 m above the water.

You should find that they are equal.

thanks, that makes sense, any ideas for the 1st one tho? i just know no matter can enter or leave, so i'm gettin confused how their can be an increase in energy

Diane_
Homework Helper
Well, there's only one choice there that could increase the energy of a closed system - emphasis on the word "closed". One of them could increase the energy, but only if the system were open. The other two don't say anything about the total energy of the system.

Is this enough?

hm my guess is Work has been done on the system but then again i'm notsure.

Diane_
Homework Helper
If work is done on the system, then it isn't closed, is it?

aw nuts, my next choice would of been kintetic, because i wouddt even know how mass would change into energy

Diane_
Homework Helper
Fission? Fusion? Antimatter?

HallsofIvy