# Energy Conversions calculations question (1 Viewer)

#### leehuan

##### Well-Known Member
Have no idea how to do this one. Apparently the answer is B.

Is this hsc

#### Fizzy_Cyst

##### Well-Known Member
Have no idea how to do this one. Apparently the answer is B.
View attachment 33401
I haven't done the calculations, the approach should be as follows:

Find the loss of Ep (just use mgh)
Find the gain in Ek (use 1/2mv^2)

Loss of Ep - Gain in Ek = energy loss (or other forms of energy)

#### InteGrand

##### Well-Known Member
The above by Fizzy_Cyst is what I was doing too, but it is an answer well smaller than the one leehuan said is apparently the right answer.

It would be:

mgh – 1/2 mv^2 = m(g – 1/2 v^2) (as h = 1)

= 0.1 * (g – 1/2 v^2).

Since v = 3.8, v^2 = (4 – 0.2)^2 = 16 – 1.6 + 0.04 = 14.44 (didn't have calculator on hand lol).

So we'd get the answer to be: 0.1 (9.8 – 7.22) =~ 0.1*(2.6) = 0.26. So the answer is much smaller than B), and should be D) I think... . leehuan, how do you know the answer is B)? Was there any working too, or just the answer given?

#### leehuan

##### Well-Known Member
At this point almost everyone I've consulted has said the answer is B. And by the exact same reasoning which I agree with.

Yeah, sometimes I question the reliability of the people who ask me (or rather 'us') questions.

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#### Fizzy_Cyst

##### Well-Known Member
How have they explained the answer as being B?

It's an impossible answer!

Change in Ep is only mgh = 0.1x9.8x1 = 0.98J. Can't get 3.7J transformed into other types of energy if there is only 0.98J to play around with in the beginning, it violates LOCOE!

Answer is definitely D.

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#### leehuan

##### Well-Known Member
I'm trying to get the source of the Q.

#### Fizzy_Cyst

##### Well-Known Member
I just had a look through my papers as I thought i recognised the font.

It's from the 2013 Exam Choice Paper, the answer is D in the marking criteria.

/high5sintegrand lol

#### Nailgun

##### Cole World
I just had a look through my papers as I thought i recognised the font.

It's from the 2013 Exam Choice Paper, the answer is D in the marking criteria.

/high5sintegrand lol
and now I have a whole new set of past papers that I need to do lol

I hope the other questions are of similar trickiness lol

#### leehuan

##### Well-Known Member
Don't blame me if people messed up reading the answers or something

But I'll let the other people that did the question know

#### Fizzy_Cyst

##### Well-Known Member
and now I have a whole new set of past papers that I need to do lol

I hope the other questions are of similar trickiness lol
Nah, Exam Choice are usually pretty straight forward. They have the odd good question here and there, but most are pretty standard.