Question

hjhkjh

Answer 1

@nincompoop

please help?

Answer 2

@ganeshie8

@whpalmer4

@ranga

anyone?

Answer 3

nvm...think I figured it out..it was 10.5 kj..i converted grams incorrectly..

Answer 4

thanks @ranga for popping in :)

Answer 5

Yes, 10.45 KJ rounded to 10.5 KJ.

Answer 6

I like to unit conversions by fractions, which gives me a built-in check for correctness.

\[1000 \text{ g} = 1 \text{ kg}\]Divide both sides by \(1000 \text{ g}\) as we are planning to go from g to kg.
\[\frac{1000\text{ g}}{1000 \text{ g}} = \frac{1 \text{ kg}}{1000\text{ g}}\]\[1 = \frac{1 \text{ kg}}{1000\text{ g}}\]We can multiply by 1 with impunity, so we can multiply by that fraction without changing the equality, but we safely convert the units when we do so.

\[50 \text{ g}*\frac{1\text{ kg}}{1000\text{ g}}*4180\frac{\text{ J}}{\text{ kg }^\circ \text{K}} * (348 ^\circ\text{K}-298^\circ\text{K}) =\]\[\qquad = 50 \cancel{\text{ g}}*\frac{1\cancel{\text{ kg}}}{1000\cancel{\text{ g}}}*4180\frac{\text{ J}}{\cancel{\text{ kg }}\cancel{^\circ \text{K}}} * (348 \cancel{^\circ\text{K}}-298\cancel{^\circ\text{K}}) \]\[\qquad=\frac{50*4180*(348-298)}{1000} \text{ J} = 10450 \text{ J} * \frac{1\text{ kJ}}{1000\text{ J}} = 10.45 \text{ kJ}\]

If you do it like this, and do the unit canceling with a skeptical eye, you'll get units which don't make sense if you haven't set up the conversion properly (divided when you should have multiplied, for example, or didn't multiply by a conversion enough times if you have a unit squared or cubes). It's a little bit more work, but less work than repeating the problem because you muffed it the first time!