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Warm-Up Exercise for lecture 5

Due 8:00 am, Tues, 15 Sep 2009

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

Newton's first law states that, in the absence of any forces, an object in motion will
☐ remain in motion forever
☐ eventually come to rest.

The engine on a fighter airplane can exert a force of 105,840 N (24,000 pounds). The take-off mass of the plane is 16,875 kg. (It weighs 37,500 pounds.) If you mounted this aircraft engine on your car, what acceleration would you get? (Please use metric units. The data in pounds are given for comparison. Use a reasonable estimate for the mass of your car. A kilogram mass weighs 2.2 pounds.)
☐ less than 10 m/s
☐ between 10 and 100 m/s
☐ between 100 and 200 m/s
☐ more than 200 m/s

If I push on an object which is at rest (like the wall), then the force exerted by my hand on the object will be equal to the force exerted by the object on my hand. However, if I push on an object, causing it to accelerate, then the force exerted by my hand on the object will be
☐ greater than
☐ less than
☐ still equal to
the force exerted by the object on my hand.

Ralph asked me a question the other day: suppose he's driving his car and a bug hits his windshield. The bug is totally smashed, but the windshield is unaffected. Doesn't this mean that the force exerted by the windshield on the bug is greater than the force exerted by the bug on the windshield? How would you answer his question?

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?

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