A small electric immersion heater is used to heat 100 g of water for a cup of instant coffee. The heater is labeled “200 watts” (it converts electrical energy to thermal energy at this rate). Calculate the time required to bring all this water from 23.0 C to 100 C, ignoring any heat losses.

A cup of hot coffee sits on your desk. Assume that the thermal energy in the coffee can be converted with an efficiency of 100%% to gravitational potential energy of the coffee-Earth system-enough so that the coffee rises up above the rim of the cup. Let the height of the coffee rise by 3.4 cm. Find the magnitude of the drop in temperature needed to accomplish this energy conversion. Use c = 4180 J/kg⋅C for coffee.

A mass m of steam at 130º C is used to warm 200 gm of water from 20º C to 50º C.  Write an expression in terms of mass, m, for the heat lost by the steam as it cools to its boiling point.  Write an expression in terms of mass, m, for the heat lost as the water condenses from the steam and then cools to the final equilibrium temperature of 50º C. Then calculate the amount of heat gained by the water, Q gained, raising its temperature from 20º C to 50º C and find the initial mass of the steam needed to complete this process as described.

A hot water heater in a residential home runs for an average of 2.2 hours per day with a heat energy input of 3.7 kW. What would be the annual cost for hot water in this home using a gas hot water heater if the cost of natural gas is $0.33/m3? The gas water heater can get 23 MJ of energy from 1 m3 of natural gas. [round your final answer to zero decimal places]?