1/23 Physics class and homework due 1/30

Hi folks,

Last week we did a nice conceptual overview of what energy is and this week we got a bit more into the nitty gritty and mathematics behind energy. We introduced the concept that energy is the ability to do work and that work is equal to force times distance. To make that more concrete, we went outside and pushed my car again. This time, however, we measured the amount of force it took to move the car and measured how much time it took to move it. Using those measurements we calculated the energy it took for us to move the car and we found how many Watts and how much horsepower we used.

In my opinion the text that we're using goes into too little detail on energy. I'm including my Energy eBook to help supplement the text

Homework due next is to

Read the Defining Energy chapter in the eBook

In the Conceptual Physics text book do Plug and Chug Pg 120 #'s 1 and 3

And Think and Solve # 2, 4

I've included the answers for the problems below.


Plug and Chug

1. 20 x 3.5 = 70J


3. First find work from question #2.

500N x 2.2m = 1100J

Then take 1100 J/2 = 550W


Think and Solve

2. Twice the power would be 1/2 the time. So the answer is 5 s.


4. So the car starts with 40,000,000 J. If the car is 25% fuel efficient that means that only 25% of that goes to making the car move so only 10,000,000 of the energy is used. So now, plug n chug.

10,000,000 = 1000 x D

10,000 m = D Or 10 Km