# Warm-Up Exercise for lecture 2

## Due 8:00 am, Thurs, Sep 3

Physics 105, Fall 2009

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

If I throw a ball straight up into the air, we say the ball is an object in "free fall"
☐ on its way up
☐ on its way back down
☐ both on its way up and on its way back down.

A ball tossed vertically upward rises, reaches its highest point, and then falls back to its starting point. During this time, the acceleration of the ball is always
☐ in the direction of motion
☐ opposite its velocity
☐ directed downward
☐ directed upward

I throw a ball across an open field. At what part of its path does the ball have a minimum 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.

Ralph asked me a question the other day. Consider a car accelerating forward. Its acceleration is 1.8 m/s2. During the first second, the car accelerates from 0 to 1.8 m/s. Ralph thought that since the velocity at the end of the first second is 1.8 m/s, the car would travel 1.8 m during that first second. But someone told him that the answer is actually 0.9 m. Can you help Ralph understand why? Don't just say, "Because the formula in the book says so."

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?