Chapter 5: Q4 (page 206)
Tarzan swings back and forth on a vine. At the microscopic level, why is the tension force on Tarzan by the vine greater than it would be if he were hanging motionless?
As the vine stretches more, that pulls up more Tarzan.
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A small block of mass is attached to a spring with stiffnessand relaxed lengthL.The other end of the spring is fastened to a fixed point on a low-friction table. The block slides on the table in a circular path of radiusR > L. How long does it take for the block to go around once?
In each of the following cases identify all objects in the surroundings that exert forces on the system, and draw a free-body diagram for the system. Assume that air resistance is negligible. (a) You hit a baseball with a bat. Choose the baseball as the system, and consider the instant of contact with the bat. (b) You are playing with a yo-yo. Choose the yo-yo as the system. As the yo-yo moves downward, you pull up on the string.
A ball of unknown mass mis attached to a spring. In outer space, far from other objects, you hold the other end of the spring and swing the ball around in a circle of radius 1.5 mat constant speed.
(a) You time the motion and observe that going around 10times takes 6.88 s. What is the speed of the ball?
(b) Is the momentum of the ball changing or not? How can you tell?
(c) If the momentum is changing, what interaction is causing it to change? If the momentum is not changing, why isn't it?
(d) The relaxed length of the spring is 1.2m, and its stiffness is 1000 N/m. While you are swinging the ball, since the radius of the circle is 1.5m, the length of the spring is also 1.5m.What is the magnitude of the force that the spring exerts on the ball?
(e) What is the mass mof the ball?
In each of the following cases identify all objects in the surroundings that exert forces on the system, and draw a free-body diagram for the system. Assume that air resistance is negligible. (a) You hit a baseball with a bat. Choose the baseball as the system, and consider the instant of contact with the bat. (b) You are playing with a yo-yo. Choose the yo-yo as the system. As the yo-yo moves downward, you pull up on the string.
You're driving a vehicle of mass 1350kgand you need to make a turn on a flat road. The radius of curvature of the turn is. The coefficient of static friction and the coefficient of kinetic friction are both 0.25.
(a) What is the fastest speed you can drive and still make it around the turn? Invent symbols for the various quantities and solve algebraically before plugging in numbers.
(b) Which of the following statements are true about this situation?
(1) The net force is nonzero and points away from the centre of the kissing circle. (2) The rate of change of the momentum is nonzero and points away from the centre of the kissing circle.
(3) The rate of change of the momentum is nonzero and points toward the centre of the kissing circle.
(4) The momentum points toward the centre of the kissing circle.
(5) The centrifugal force balances the force of the road, so the net force is zero. (6) The net force is nonzero and points two and the centre of the kissing circle.
(c) Look at your algebraic analysis and answer the following question. Suppose that your vehicle had a mass five times as big. Now what is the fastest speed you can drive and still make it around the turn?
(d) Look at your algebraic analysis and answer the following question. Suppose that you have the originalvehicle but the turn has a radius twice as large (152 m). What is the fastest speed you can drive and still make it around the turn? This problem shows why high-speed curves on freeways have very large radii of curvature, but low-speed entrance and exit ramps can have smaller radii of curvature.
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