Ch13_1
Practice Problems


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1) A constant force of N acts tangentially on the wheel shown which has a cm radius. The wheel axis through the center point is inserted into a hole where it has a tight fit causing friction which generates heat. How much heat in calories is generated during turns (see sheet 3; calculate the work done by the force against the frictional torque- see sheet Ch 8 sheet 38) ?

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2) A kg person runs times up the stairs to the D level of the Physics Building. Assume for simplicity that the energy spent is equal to the gain in potential energy for the m height. How many nutritional calories has the person used up (see sheet 3) ? Indicate with a positive (negative) sign whether under your simplifying assumption it does (does not) matter if the person walks or runs the distance.
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3) A bridge made of steel and km long undergoes temperature changes from oF to oF. By how much does the length of the bridge change due to thermal expansion (see sheet 4; use 11x10-6 oC-1 for the coefficient of linear expansion of steel) ? Indicate with a positive (negative) sign whether the length increases ( decreases ) with rising temperature.
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4) The temperature of liters of water is raised by oC. What is the heat input in calories (see sheet 8,11) ? Indicate with a negative (positive) sign whether for the same mass in steel less (more) calories are needed to produce the same temperature rise (use 0.107 cal g-1 oC-1 for the specific heat of steel).
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5) grams of steel at oC is put into liter of water at 20 oC. What is the final temperature at equilibrium assuming no heat loss to the environment (see sheet 12; use 0.107 cal g-1 oC-1 for the specific heat of steel) ? Indicate with a positive (negative) sign whether the steel looses less (the same amount of) heat than the water gains.
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6) grams of ice are added to grams of water at a temperature of oC. How much ice is left over at equilibrium. (see sheet 14,17,18) (Use 79.7 cal/g for the latent heat of fusion of water) ? Indicate with a positive (negative) sign whether the final temperature is greater than zero (is zero) oC.

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