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sol05 - We have to be careful to include the directions of...

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PHYSICS 103 Chapter 2 -- HW #5 Questions 40. In a vacuum the two balls would fall with the same acceleration. However, in air the rubber ball will be affected more by the air resistance and have a smaller acceleration. The rubber ball will therefore lag behind. 52. A ball rolling up and down a ramp is very much like a ball thrown vertically upward. The acceleration is constant in size and direction during the entire motion. Galileo used this fact to conclude that free fall was motion with a constant acceleration. The downward acceleration causes the ball to slow down when moving upward and to speed up when moving downward. Be careful : The acceleration at the top of the path is not zero; it is the same as for the rest of the path. Exercises 20. We use the definition of the acceleration to solve this problem.
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Unformatted text preview: We have to be careful to include the directions of the velocities. In the case of one-dimensional motion, we can use plus and minus signs to indicate the directions. ( 29 ( 29 ( 29 2 10 m s 30 m s 4 s is up 10 m s f i v v t a---= = = +-You can also reason this out in two steps. On the way up it is slowing down at a rate of 10 m/s 2 , so it will take three seconds to reach the top where the speed is zero. On the way down, it is speeding up at the same rate, so it will take one additional second to attain the velocity of 10 m/s downward. 22. We use our equations for one-dimensional motion. ( 29 ( 29 2 10 m s 4 s 40 m s f v a t = = = ( 29 ( 29 2 2 2 1 1 2 2 10 m s 4 s 80 m d a t = = = or 40 m/s 20 m/s 2 2 i f v v v + + = = = ( 29 ( 29 20 m/s 4 s 80 m d vt = = =...
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