# Warm-Up Exercise for lecture 4

## Due 8:00 am, Thurs, Sep 11

Physics 105, Fall 2008

Enter your 3-digit class identification number:

Enter the last 4 digits of your BYU ID:

Did you complete the reading assignment?  (Typically this means at least 20-30 minutes looking over the assigned sections of the book.)
☐ yes ☐ no

I throw a ball at an upward angle across a flat field. Neglecting air resistance, at what part of its path does the ball have its maximum speed?
☐ right before it hits the ground
☐ halfway to the top
☐ at the top of its path
☐ right after it leaves my hand
☐ There's not enough information to say

In 2D projectile problems, usually you use equations from one of the directions to figure out the time the projectile is in the air. (Look over the book examples, see if they do this.)
☐ True
☐ False

Neglecting air resistance, at what angle should you throw a ball on a flat field in order to get the maximum range?
☐ 30°
☐ 45°
☐ 60°
☐ It depends on the initial speed

Ralph asked me a question the other day about a ball that is thrown upwards at an angle. Ralph thought that since the ball is still moving upwards for a while after it is thrown, it must have some upwards acceleration in the air after it leaves my hand that continues to propel the ball. I told him "No, that's not quite what is happening." Can you help Ralph understand what is happening?

The comments in the next next two boxes go into a big, mostly anonymous text file that I skim through before the morning lecture, using the comments to help me plan class discussion. ("Mostly anonymous", because I can track down who made what comment, but it takes some effort on my part to do so.) Therefore, if you really want to make sure I see your question/comment and answer it individually, you should send it to me via email and not through this form.

Which part of today's assignment was particularly hard or confusing? What would you like to spend extra time on in class?