## Chapter 8 Question #3 (The First Law) [ENDORSED]

$\Delta U=q+w$

Jonathan Orozco 1A
Posts: 9
Joined: Wed Sep 21, 2016 2:58 pm

### Chapter 8 Question #3 (The First Law)

Hi everyone, i was wondering if anyone could help me solve number 3 from the homework problems.

Question 3: Air in a bicycle pump is compressed by pushing in the handle. If the inner diameter of the pump is 3.0 cm and the pump is depressed 20.cm with a pressure of 2.00 atm, (a) how much work is done in the compression? (b) Is the work positive or negative with respect to the air in the pump? (c) What is the change in internal energy of the system?

I have no idea on how to start this problem if anyone can help i appreciate it and thank you in advance.

Brandon Ho 1J
Posts: 21
Joined: Wed Sep 21, 2016 3:00 pm

### Re: Chapter 8 Question #3 (The First Law)  [ENDORSED]

Since w = -P(change in volume), we first have to calculate the change in volume. Since we know the radius (from the diameter) and the distance the pump is compressed, we can find the change in volume through -(pi)(r^2)(d). We then convert this to liters using (1L / 1000 cm^3). Then we can plug everything into our work equation and convert L x atm into joules using (101.325 J / L x atm). Hope this helps you get started!