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Monday 8/27 Pretest 1 due Pretest 2 posted Monday 9/3 Labor Day No Class Pretest 3 posted Tuesday Tuesday Wednesday 8/29 HW 1 due HW 2 posted Wednesday 9/5 HW 3 posted HE 1 posted Thursday Thursday Friday 8/31 Pretest 2 due Friday 9/7 HW 2 due Physics 100 Fall 2007 You are throwing a ball straight up in the air. At the highest point, the ball's A. velocity and acceleration are zero. B. velocity is nonzero but its acceleration is zero. C. acceleration is nonzero, but its velocity is zero. D. velocity and acceleration are both nonzero. Physics 100 Fall 2007 Answer C Quantitative Description of Motion
Constant velocity (no acceleration) Position = starting position + velocity time x = x0 + vavg t Velocity = starting velocity v = v0 Constant acceleration (falling) Position: x = x0 + v0 t + () a t 2 Velocity = starting velocity + acceleration time v = v0 + a Average velocity: vavg = v0 + () a
Physics 100 Fall 2007 t t Question 5 Does a ball's horizontal motion affect its fall? Why does a thrown ball travel in an arc? Physics 100 Fall 2007 Throws and Arcs I Gravity affects only the ball's vertical motion A ball coasts horizontally while falling vertically The two motions are independent Physics 100 Fall 2007 Throws and Arcs II
The rate at which a body falls is unaffected by its horizontal velocity. Physics 100 Fall 2007 Consider the situation depicted here. A dart gun is accurately aimed at a dangerous criminal hanging from the gutter of a building. The instant the gun is fired and the dart moves with a speed v0, the criminal lets go and drops to the ground. What happens? The dart A. hits the criminal regardless of the value of v0. B. hits the criminal only if v0 is large enough. C. misses the criminal.
Physics 100 Fall 2007 Answer A Correct Answer: A Throws and Arcs III
At what angle should one throw? To get large `hang time', launch at > 45 To get to target fastest, launch at < 45 To get greatest distance, launch at 45 (neglect air resistance) Physics 100 Fall 2007 Summary About Falling Balls Without gravity, a free ball would coast With gravity, an otherwise free ball experiences its weight, accelerates downward, and its velocity becomes increasingly downward Whether going up or down, it's still falling Its horizontal coasting motion is independent of its vertical falling motion
Physics 100 Fall 2007 ...
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- Fall '07
- Acceleration, Velocity, Week-day names