02-203-08hwk-Ch02

02-203-08hwk-Ch02 - 02-203-07hwk-Ch02 1 Chapter 2...

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Unformatted text preview: 02-203-07hwk-Ch02 1 Chapter 2: One-Dimensional Kinematics Solutions to Problems 3. Picture the Problem : The ball is putted in the positive direction and then the negative direction. Strategy: The distance is the total length of travel, and the displacement is the net change in position. Solution: (a) Add the lengths: ( ) 10 2.5 m 2.5 m 15 m + + = (b) Subtract x i from x f to find the displacement. 10 0 m 10 m f i x x x Δ =- =- = Insight: The distance traveled is always positive, but the displacement can be negative. 13. Picture the Problem : The nerve impulses propagate at a fixed speed. Strategy: The time elapsed is the distance divided by the average speed. The distance from your finger to your brain is on the order of one meter. Solution: Divide the distance by the average speed: 2 1 m 0.010 s 1 10 m/s d t s = = = × Insight: This nerve impulse travel time is not the limiting factor for human reaction time, which is about 0.2 s. ------------------------------------------------------------------------------------------------------------------------------ 29. Picture the Problem : The runner accelerates uniformly along a straight track. Strategy: The change in velocity is the average acceleration multiplied by the elapsed time. Solution: 1. (a) Multiply the acceleration by the time: ( ) ( ) 2 0 m/s 1.9 m/s 2.0 s 3.8 m/s v v at = + = + = 2. (b) Multiply the acceleration by the time: ( ) ( ) 2 0 m/s 1.9 m/s 5.2 s 9.9 m/s v v at = + = + = Insight: World class sprinters have top speeds over 10 m/s, so this athlete isn't bad, but it took him a whole 5.2 seconds to get up to speed. He should work on his acceleration! ------------------------------------------------------------------------------------------------------------------------------ 38. Picture the Problem : The particle travels in a straight line in the positive direction while accelerating in the positive direction (speeding up). Strategy: Use the constant acceleration equation of motion to find the initial velocity. Solution: Solve equation 2-7 for v : ( ) ( ) 2 9.31 m/s 6.24 m/s 0.300 s 7.44 m/s v v at = - =- = Insight: As expected the initial velocity is less than the final velocity because the particle is speeding up....
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02-203-08hwk-Ch02 - 02-203-07hwk-Ch02 1 Chapter 2...

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