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Chapter 8: Q.9 (page 199)
Suppose the moon were held in its orbit not by gravity but by a massless cable attached to the center of the earth. What would be the tension in the cable? Use the table of astronomical data inside the back cover of the book
The tension in the cable is.
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The physics of circular motion sets an upper limit to the speed of human walking. (If you need to go faster, your gait changes from a walk to a run.) If you take a few steps and watch
what鈥檚 happening, you鈥檒l see that your body pivots in circular motion over your forward foot as you bring your rear foot forward for the next step. As you do so, the normal force of the
ground on your foot decreases and your body tries to 鈥渓ift off鈥� from the ground.
a. A person鈥檚 center of mass is very near the hips, at the top of the legs. Model a person as a particle of mass m at the top of a leg of length L. Find an expression for the person鈥檚 maximum walking speed vmax.
b. Evaluate your expression for the maximum walking speed of a 70 kg person with a typical leg length of 70 cm. Give your answer in both m/s and mph, then comment, based on your
experience, as to whether this is a reasonable result. A 鈥渘ormal鈥� walking speed is about 3 mph.
A model rocket is resting horizontally at the top edge of a -high wall when it is accidentally bumped. The bump pushes it off the edge with a horizontal speed of m/s and at the same time causes the engine to ignite. When the engine fires, it exerts a constant horizontal thrust away from the wall.
a. How far from the base of the wall does the rocket land?
b. Describe the rocket鈥檚 trajectory as it travels to the ground
Mass on the frictionless table of FIGURE EX8.13 is connected by a string through a hole in the table to a hanging mass . With what speed must rotate in a circle of radius if is to remain hanging at rest?
FIGURE EX8.13
What is free-fall acceleration toward the sun at the distance of the earth鈥檚 orbit? Astronomical data are inside the back cover of the book .
Ramon and Sally are observing a toy car speed up as it goes around a circular track. Ramon says, 鈥淭he car鈥檚 speeding up, so there must be a net force parallel to the track.鈥� 鈥淚 don鈥檛 think so,鈥� replies Sally. 鈥淚t鈥檚 moving in a circle, and that requires centripetal acceleration. The net force has to point to the center of the circle.鈥� Do you agree with Ramon, Sally, or neither? Explain.
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