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This is a physics question, but it's calculations.

A 15kg child slides down a 2.3m -high playground slide. She starts from rest, and her speed at the bottom is 2.1m/s .

What is the change in the thermal energy of the slide and the seat of her pants? (2.s.f.)

I used the kinematics equation

$$d= \frac{(v_i+v_f)}{2} * (t)$$

$$2.3 = \frac{2.1 \cdot t}{2}$$

$$t= 2.19$$

Then I used t to find acceleration then multiply acceleration with the mass which is 15kg, and then multiply that again by 2.3m to find the change in thermal energy. But I feel like I calculate t incorrectly, because it keeps telling me it's incorrect. The rest is correct, however, the first part is not.

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  • $\begingroup$ Firstly, this is a physics question. Secondly, in your first sentence, you seem to imply that mathematics is calculations - and that is not correct. Finally, your error is not in your calculations, but in your setup. The relevant ideas are conservation of energy, potential energy, and kinetic energy. You don't need to use any kinematics $\endgroup$ – davidlowryduda Oct 19 '13 at 2:41
  • $\begingroup$ I keep getting the answer 30m/s but it says it is incorrect $\endgroup$ – Sherry Eskandarian Oct 19 '13 at 3:42
  • $\begingroup$ I got the answer, thank you $\endgroup$ – Sherry Eskandarian Oct 19 '13 at 3:58
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The answer to this question is 305m/s but to 2.s.f it is 310m/s

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  • $\begingroup$ If you are satisfied, you could accept your answer (I think you have to wait a day) so it gets off the open list. $\endgroup$ – Ross Millikan Oct 19 '13 at 4:09
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It's conservation of energy -- you don't need any calculus. You know that in the absence of friction energy is conserved. If some energy is lost it must have gone to friction -- a.k.a thermal energy. You know how much energy lost because the child starts at some height from rest. That tells you the initial energy (her potential energy.) I think you can take it from there.

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