which has the most stored energy? (for my lecture notes)?

Question

A 5kg weight 1m above the floor  (PE)
A 45g golf ball travelling at 40 m/s (KE)
A jam doughnut 250kcal (Calories)
A spring compressed 0.1 m by a force of 20kg.
A cup of coffee (black, no sugar) 0.12litres 40 deg above ambient
A Duracell D cell 1.5V 15Amp hours
A bicycle wheel spinning at 10 rps. dia 21cm, mass 0.2kg

I have worked out answers but I don't believe the results - so if someone would be kind enough to check them for me that would be great.  I haven't provided the equations or working in case I have one wrong.

Bramble · Accepted Answer

1) 5 x 9.81 x 1 = 49 J
2) 0.045 x 40² x ½ = 36 J
3) 250 kcal = 250 x 4184 = 1046 x 10^6 J
4) 0.1 x 20 x 9.81 x ½ = 9.8 J
5) 4184 x 0.12 x 40 = 20 x 10³ J
6) 1.5 x 15 x 3600 = 81 x 10³ J
7) 0.2 x 4 x π² x 100 x 0.21² x ½ = 17.4 J

So the jam doughnut takes it; unless of course the 5 kg weight is composed of jam doughnuts.

Edit:

No I can't spot your error but I do see mine:

3. Obviously I forgot the decimal point in the 1045 - it should read 1.046

7. I think I have used the diameter where I should have used the radius so I should get 4.35 J. I'm used to bigger bicycle wheels I guess!

I think your only "mistake" is in approximation, which is of course insignificant in this problem!

Sorry for any confusion caused.

which has the most stored energy? (for my lecture notes)?

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