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What’s Most Difficult Right now I am finding remembering stuff from old classes...its too early in the semester =). I took trigonometry last summer and i passed it with flying colors, but then looking at problems, i totally forgot how to do SIN, and COS. Once I look at the problem though it comes to me...it just takes me a while. Otherwise nothing is that difficult right now. =) There are no problems thus far. Finding positive and negative velocities on a graph. Im having trouble keeping my thoughts straight on what is velocity and what is acceleration. The problems aren't really all that difficult as of yet. I'm just having trouble getting my brain back in to the swing of things. telling the difference on a line graph between acceleration and velocity 05
Review • Kinematics : Description of Motion • Position • Displacement • Velocity • average • Instantaneous • Acceleration • average • instantaneous 07
Acceleration Units • Speed/time • m/s/s = m/s2 • mi/hr/s = mi/hr-s • km/hr/s = km/hr-s • Distance/time/time • or distance/time2
The Ninja • The Ninja motorcycle can accelerate from 0 to 60 mi/h in 3.8 s. • What is its average acceleration? • 15.8 mi/h/s • 23 ft/s/s or 7 m/s/s
Preflight 4.1 (A) (B) (C) Which x vs t plot shows positive acceleration? 86% got this correct!!!! “The slope of the graph is getting increasingly positive; the velocity is increasing over time.” 08
Equations for Constant Acceleration(text, page 34) • v = v0 + at • vav = ½ (vo + v) • x = x0 + v0t + ½ at2 • v2 = v02 + 2a(x-x0) 10
Correct x=1/2 at2 Correct v=at Acceleration ACT An car accelerates uniformly from rest. If it travels a distance D in time t then how far will it travel in a time 2t ? A. D/4 B. D/2 C. D D. 2D E. 4D Follow up question: If the car has speed v at time t then what is the speed at time 2t ? A. v/4 B. v/2 C. v D. 2vE. 4v 24
# 43 Ch 2 • A cheetah can accelerate from rest to 25.0 m/s in 6.22 s. Assuming constant acceleration, • A. how far has the cheetah run in this time? • B. after sprinting for just 3.11 s, is the cheetah’s speed 12.5 m/s, > 12.5 m/s, or < 12.5 m/s? • C. what is the cheetah’s average speed for the first 3.11 s? • D. calculate the distance covered by the cheetah in the first 3.11 s.