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Unformatted text preview: Problem 1 The graph below represents the position of an object as a function of time: For each labeled point, indicate what the graph tells you about the velocity and acceleration at that
time by circling the appropriate choices: Velocity Acceleration ﬁ Point A negative zero negative zero
E PointB negative zero zero positive
(k PointC zero positive negative positive
8‘ PointD negative positive negative zero
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The graph on the left below show velocity as a function of time, i.e. v(t).
Make a sketch on the right showing a possible graph of position as a function of time which is
consistent with that v(t).
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shown here: The sled and you together have a mass of 75 kg. Once you are seated in the sled at rest, you pick up your feet and the sled starts accelerating down the hill. As it goes, there is a constant friction force
of 65 N between the snow and the sled. 1,, mg (a) Draw a free—body diagram for the sled.
I, Pqﬂ, (b) What is the magnitude of the downhill acceleration?
(c) How much time does it take the sled to reach the bottom of the hill?
(d) What is the sled’s speed when it reaches the bottom of the hill? At the bottom of the hill, the sled transitions smoothly to a horizontal field, initially keeping the
same speed. There is now a constant friction force of 75 N as it glides across this field. (9) Measuring from the base of the hill, how far does the sled travel horizontally before coming to
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vertical distance from your hand to your dog’s mouth is 3.4 m, and the horizontal distance is 5.5 m. (a) Assuming that you toss the ball with an initial downward angle of 15" relative to the horizontal, HS and you want your dog to catch the ball in its mouth without having to move, what speed should you give the ball when you toss it? (b) What angle does the ball’s velocity vector have (relative to the horizontal) at the moment your
dog catches it? (c) Suppose that instead of the speed you found in part (a), you throw the ball with a speed of
13 11115, but with the same initial downward angle of 15°. Your dog jumps straight up to catch the ball in its mouth. How high did she have to jump? (That is, when she catches the ball in her mouth,
how high is her mouth above its initial position before the jump.) pa_. (This Is like
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60 dog has 7%; JIM/1p Verﬁ'm/O/ (“2H "7) “(J‘1’”) = IO M Problem 4 The Earth follows a slightly elliptical orbit around the Sun, However, for this problem, assume it follows a uniform circular orbit with a radius equal to the average Earth~Sun distance. The period of
the orbit is, of course, equal to one year. 6 POMIB (a) In what direction is the Earth accelerating? 7 Pow; (b) What is the magnitude of the Earth’s acceleration? Write your answer with units of m/sz. 7 (6) Where is the center of mass of the SunEarth system? CG) RWOH’J 7%6 50M. (6) Ceﬂl'w‘pefaI/ acre/erah‘on: :L
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it to the base of the wedge. Block A has a mass of 5 kg, block B has a mass of 4 kg, and the Spring has a spring constant of 3.5 N/cm. Assume that there is no friction between the blocks and the wedge, and that the string and
pulley are massless and frictionless. The system is initially at rest. (a) What is the tension in the string? (b) Is the spring stretched or compressed? By how much? Suddenly, the spring comes apart from block A, freeing it to move. (c) What is the acceleration of block A? In which direction? (d) What is the tension in the string now? (3) What is the acceleration vector for the center of mass of the block—string—block system? {6 (1+ rest so 146% ’EM’CQ on Hock B tab/54 59 Zero. ‘r/
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This note was uploaded on 11/11/2008 for the course PHYS PHYS171 taught by Professor Shawhan during the Fall '07 term at Maryland.
 Fall '07
 Shawhan
 mechanics

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