Physics 157 Midterm 1 2017
1. A length of nylon fishing line of 2 mm diameter is tied to a length of 0.5 mm diameter
stainless steel wire, then stretched between two rigid supports 2 m apart such that the
tension in the wires is 20 N and the connection point between the two wires is exactly
midway between the posts. The air temperature then goes down by 20 C. Find the
distance that the connection moves.
[Youngs modulus for nylon is 3 GPa, its thermal expansion coefficient is 6⇥10 5 /K. Youngs
modulus for stainless steel is 180 GPa, its thermal expansion coefficient is 1.7 ⇥ 10 5 /K.]
2. A UBC engineering student working for a solar panel company is asked to design a
square solar panel which is 20% efficient. The panel is required to bring 500 ml water
to the boiling point in 10 minutes from an initial temperature of 20 C during a summer
day (in Vancouver) at noon time when the panel is under direct sunlight. Determine the
minimum length of each side of the square solar panel.
Useful Constants: Solar constant is 1kW/m2 , Specific Heat of water cwater = 4190J/kg K.
3. A Starbucks chemical engineer wants to design the perfect iced co↵ee drink. This drink
is to be served at temperature of 0 C and contain 25% crushed ice by mass. Initially the
engineer starts with 200 grams of co↵ee at 80 C and mixes in crushed ice at temperature
of 10 C. Find the initial amount of crushed ice to add in order to obtain the desired
drink.
(Neglect the heat capacity of the cup and heat exchange with the environment.)
Useful Constants: cice = 2100J/kg K, cwater = 4190J/kg K, Lfusion water = 334, 000J/kg.
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