intro physics HW
1) Unless a phase change occurs, when a substance absorbs energy its temperature will
rise. Imagine two samples of water, one twice as massive as the other, that in separate
experiments absorb the same amount of energy from a heater.
a) Will each sample undergo the same temperature change? If not how will the observed
temperature changes differ? Explain your reasoning.
b) How can your answer to part a be explained using an atomic/molecular model of the
water samples (i.e. thinking of the water samples as groups of identical particles)?
2) A 75 gram sample of aluminum is heated to 100 °C and then placed in a well insulated
container filled with a large volume of water. The aluminum/water mixture reaches an
equilibrium temperature of 21 °C.
a) How much energy (in either calories or Joules) did the aluminum lose? Show your work.
b) How much energy did the water gain during the experiment? Explain your reasoning.
3) It takes 1 calorie of energy to change the temperature of 1 gram of water by 1 degree Celsius. That is, the specific heat of water is 1·cal/(gr ?C)!. This is the c in the equation: Q=mc?T. It takes 539 calories to convert 1 gram of liquid water into steam at 100 °C.
This is the latent heat which is the L in the equation: Q=Lm which describes the energy
required to cause m grams of a substance to undergo a phase change such as boiling.
With this in mind determine: the amount of energy that 50 grams of water must absorb if it is to be heated from 20 °C to its boiling point and then be completely converted to
steam. Show your work.
4) A metal cup filled with liquid water initially at 20 °C is p
laced in a freezer. Describe the contents of the cup after a long time if
a) The freezer temperature is set to exactly -10 °C.
b) The freezer temperature is set to exactly 0 °C.
In each case explain your reasoning
5)If the internal energy of an ideal gas increase by 150J when 240J of work is done to compress it, how much heat is released?
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6) If the temperature of a substance does not change, and it is not undergoing a phase
change, then its internal (or thermal) energy is also constant. This would be the case
when a gas is compressed at constant temperature. Consider the situation
described in the previous question (#5). Assume the same amount of work was done to
compress the gas, but the compression occurred while the temperature of the gas
remained constant. How much heat will flow from the gas into the environment under these conditions? Explain your reasoning.
