Thermodynamics Homework 4
1st law of Thermodynamics
Name: ___________________________
Show your work and use significant figures.
1) Calculate ∆Ufor each of the following cases:
a. Q = + 51 kJ, w = - 15 kJ
b. Q = + 100. kJ, w = - 65 kJ
c. Q = - 65 kJ, w = - 20 kJ
d. In which of these cases does the system do work on the surroundings?
2) Calculate ∆Ufor each of the following:
a. Q = - 47 kJ, w = + 88 kJ
b. Q = + 82 kJ, w = + 47 kJ
c. Q = + 47 kJ, w = 0
d. In which of these cases do the surroundings do work on the system?
3) 125 kJ of energy is added to a system while 104 kJ of work is done by the system. Calculate
the change in internal energy (in kJ).
4) A system undergoes a process consisting of the following two steps:
Step 1: The system absorbs 73 J of heat while 35 J of work is done on it.
Step 2: The system absorbs 35 J of heat while performing 72 J of work.
Calculate the change in internal energy for the overall process (in J).
5.) Define the First Law of Thermodynamics.
Thermodynamics Homework 4
6.) A 20kg amateur rocket has 100N of thrust applied to it. What is the acceleration of the
rocket?
7.) You add coal to an old steam engine on a train. The coal adds 150kJ of energy into the engine.
The engine then does 120kJ of work. What is the change in internal energy of the engine?
8.)An engine does 40J of work while losing 20J of thermal energy to its surroundings. What is the
change of internal energy of the engine?
9.) You add 5000J of energy into an engine and the engine does work. The engine loses 1200J of
energy to its surroundings when doing the work. How much of the energy added to the engine is
available to do work?
10.) what is a Carnot engine?
11.) A car is traveling at 30m/s when it begins to accelerate at 2.0m/s2 for 12s. What is the final
velocity of the car?
12.) How far does the car travel during its acceleration in problem 11?
13.) A small asteroid with a diameter of 150m is traveling toward Earth. It’s mass is 3,000,000kg.
What is the force of attraction between the asteroid and a cosmonaut who’s mass is 140kg when
the cosmonaut is standing on the surface of the asteroid?
14.) A boy pushes a cart for 12m with a force of 30N. What is the work done on the cart?
15.) A box weighing 120N is being dragged on the floor which has a coefficient of friction of 0.33.
What is the frictional force between the floor and the box?