11/6 HS Physics and Homework due 11/13
Hi folks,
Today we started a unit on projectile motion. Otherwise known as 2 dimensional motion. This will include using everything we've worked with so far and putting it to use on a new set of problems. Today we took a look at a typical physics problem that goes a little something like this. If a ball is thrown off a 20 m tower and it goes 50 m how fast was the ball thrown. The point of these problems is to see how vertical velocity and horizontal velocity are independent from one another. Next week we will get a bit deeper into this concept. We also did a lab today where we brought these problems to life by measuring the distance a Hot Wheels car traveled through mid-air after being launched off of a table.
For homework this week: (Please email if you have any questions. )
Do the "Think and Solve" problems 2 - 6 on page 42. Some of these are pretty tricky so give them a shot. (I've included the answers below)
The following is based on today's lab. (Answers below)
ALSO, THERE WILL BE A QUIZ NEXT WEEK SO BE SURE YOU ARE FAMILIAR WITH ALL THE PROBLEMS AND DEFINITIONS WE'VE WORKED WITH SO FAR. The focus will be on these most recent v=d/t, v=at and d=1/2at^2 problems so be sure to master these. PAV graphs may return as well so be sure to review that also.
1. We found the horizontal velocity of the car by using the distance the car traveled. What other way could we have done this? What would be a large disadvantage to this other way.
2. The car accelerated as it zipped down the ramp. What could you have done to find the average acceleration the car had?
3. To find the horizontal velocity of the car, you used the same time over and over. What did that time represent (in other words, what was that the time for) and why was that the only time you needed?
4. What was the vertical velocity of the car when it hit the ground?
5. Make a graph where the height the car was dropped from is the x axis (the horizontal axis) and the speed the car reached is the y axis. Plot all 5 points and draw a line between each point. The following questions are based on your graph.
a. How would you describe the slope of the graph?
b. If you wanted the car to have a horizontal velocity of 4 m/s how from what height would you drop the car?
c. If you wanted the car to land exactly 2 m away from the table, what speed would the car need to have? How high would you need to drop that car from (assuming the same slope to the ramp).
Answers to lab questions.
1. We could have found the amount of time it took the car to travel the horizontal distance with a stop watch. The problem with this is that the time is so short, getting accurate measurements would be very hard.
2. If you found the amount of time it took the car to come down the ramp, you could take the velocity you found and divide it by the time. A = v/t Again, accuracy here would be tough due to the very short time.
3. That time was the time it took the car to fall from the height of the table. Since gravity doesn't care, anything falling from that height will take that amount of time to reach the ground. It doesn't matter if it's moving or not. So, no matter how fast the car was going it always took that long to hit the ground.
4. This depends a bit on the height you measured your table to be but basically if you use V=at (t being the time it took to hit the ground) you're good.
5. a. The slope is probably a fairly straight downward slope.
b. This depends on your slope but if you were to extend the slope of the line at what height does it reach 4 m/s?
c. Again, the exact answer depends on your slope but first you must find what speed it needs to reach 2 m. (v = d/t for that) Then, look back at the graph and find what height you would need to drop the car from.
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