Lab_10
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1) You do work against a constant force of F = N, which balances (is equal to in magnitude) the frictional force between the two brass cups shown, the rotating outer brass cup and the stationary inner brass cup in the sketch above. The force exerted by a string acts tangentially to the disk shown, which has an effective diameter D = cm. What is the amount of work (Ch8 sheet 38) you do via a crank that rotates the outer brass cup N = times ? (Hint: when evaluating the work, write down the torque given by the tangential force and the lever arm, which is the effective radius of the disk. Note that each turn of the outer brass cup corresponds to an angle of 2 p radians) Indicate with a negative (positive) sign whether the equation for the work, W = N F 2p D/2, is correct and follows ( is incorrect and does not follow) from the expression in Ch8 sheet 38.
2) When doing the experiment sketched above you heat up the brass containers with a combined mass mb = grams and an amount of water with a mass mw = grams. What is the amount of heat absorbed (Ch 13 sheet 8) by the cups and the water (in calories), if their initial temperature (at the start of the cranking) and their final temperature (after ending the cranking) is 0C below and above room temperature, respectively (Use the specific heats given in Table 1 of the lab manual for this experiment 10) ? Indicate with a negative (positive) sign whether the equivalent amount quoted in SI units is different from (equal to) your result in calories.
3) When doing the experiment sketched above you heat up the brass containers with a combined mass mb = 200 grams and an amount of water with a mass mw = 350 grams. What is the absolute error of the amount of heat absorbed (Ch 13 sheet 8) by the cups and the water (in calories), if their initial temperature (at the start of the cranking) and their final temperature (after ending the cranking) is 0C below and above room temperature, respectively (Use the specific heats given in Table 1 of the lab manual for this experiment 10). Assume that the error of the brass and water masses is grams and the error of the initial and final temperature is 0C each. (Hint: In Q= (mb cb + mw cw )(Tf – Ti ) calculate the error of each bracket according to expression (6) in “Error and Uncertainty” (“EU”). Note that cb and cw are factors which must be included in the absolute errors when applying (6). Then calculate the error of the product of the two brackets according to expression (7) of “EU”). Indicate with a positive (negative) sign whether you can (cannot) replace the 0C by the same number of 0K.
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