Homework Help: Physics

Posted by Elisabeth on Saturday, June 5, 2010 at 9:31pm.

A 56.6kg hiker starts at an elevation of 1270m and climbs to the top of a 2660 peak.

(I know the answers to B and C, I just have a question on A)
A) What is the change in the hikers potential energy?

I took PE=mg(h2-h1) and got (56.5)(9.8)(2660-1270)=769643J

When I checked my work with some problems on the net, I was seeing answers as large as mine and others that only used 4 digits (Like 7696J)

Why are they cutting them down, and shouldn't the unit change if they did? If the unit should change... why?

Physics - MathMate, Sunday, June 6, 2010 at 8:42am
Your calculation looks good to me, except for the number of significant digits (too many) in the answer.
You may want to review the other answers on the net to see if
1. they use different units (hJ, kJ, etc.)
2. they use scientific notation, like 7696*10²J., thereby trimming on the number of significant digits.

Also, is the hiker's mass 56.5 or 56.6?
Physics - Elisabeth, Sunday, June 6, 2010 at 1:17pm
Just a typo on my part. The hiker's mass is the same as in my equation: 56.5.

I just looked over the answers again. Most people answered the same as I did. A few of them put in scientific notation, but not like you did. they put 7.6X10^5 which doesn't make sense to me. I like your notation better. Fits the four digits. One person answered it in kJ, but the answer was only three digits long. I think I am going with the four digit scientific notation. It makes the most sense to me.

Thank you very much!
Physics - MathMate, Sunday, June 6, 2010 at 7:11pm
I personally would suggest using powers of 10 that are multiples of three (some call it the engineering notation). This makes for easier interpretation, i.e. thousands, millions, billions, etc.

So
769643J
=769.6*10^3J
=769.6kJ
=0.770*10^6J
etc.

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