How Things Work: An Introduction to Physics week 5

In this blog you will find the correct answer of the Coursera quiz How Things Work: An Introduction to Physics week 5 mixsaver always try to brings best blogs and best coupon codes

Week- 5



1. A toy top is a disk-shaped object with a sharp point and a thin stem projecting from its bottom and top, respectively. When you twist the stem hard, the top begins to spin rapidly. When you then set the top’s point on the ground and let go of it, it continues to spin about a vertical axis for a very long time. What keeps the top spinning?


2. To start a motionless toy top spinning, you twist it. What determines the direction in which the top spins?


3. You are traveling through deep space in a large spaceship and everything in the ship is weightless. The ship is experiencing zero net force and it coasts forward. However, in preparation for docking at a space station, the ship is rotating slowly. You notice that one location in the coasting ship moves at constant velocity, even as the rest of the ship rotates about that location. What is this special location in the ship?


4. A tall luxury hotel has a rotating restaurant at its top. The disk-shaped floor of the restaurant rotates slowly about the center of the restaurant and completes one full rotation every 30 minutes. When the restaurant opens each day, the manager turns on the motors that make the restaurant spin, but it takes several minutes for the restaurant to begin spinning at its full angular velocity. Why doesn’t the restaurant reach full speed immediately?


5. A modern bicycle has two pedals mounted on a rotating device known as a crank. Pushing down on one pedal with your foot produces a torque on the crank, about its pivot, except in which situation(s)?


6. Arm-wrestling is a simple game that two people can play. The players sit across from one another at a table, place their right elbows together on the tabletop and clasp their right hands together. When the competition starts, each person tries to twist the pair of arms counterclockwise from that person’s perspective until those arms touch the table. It’s a rotational problem, with the elbows acting as the pivot and the two players trying to rotate the pair of arms in opposite directions. Suppose you are arm-wrestling with a friend and you are winning. Compare the torque you are exerting on your friend to the torque that your friend is exerting on you.


7. You are arm-wrestling another friend and find that you are almost perfectly matched. Your pair of arms is vertical and motionless, even though you are both trying hard to win. To begin winning, you want that pair of arms to rotate counterclockwise from your perspective. What must you do to make that happen?


8. You are making pizza and are spinning a ball of pizza dough in midair to make a larger and larger disk. As the diameter of the disk increases, you find it more difficult to change the disk’s angular velocity. Why?


9. Your car has a flat tire and you are using an automobile jack to lift the corner of the car so that you can change the tire. The jack involves a lever and you lift the corner of the car upward by pushing the handle of the lever downward. You notice that as the handle moves downward 10 inches, the corner of the car moves upward only 0.5 inches. Assuming that the jack is not wasting any energy, compare the downward force you exert on the jack handle to the upward force that the jack exerts on the car.


10. Tower cranes are frequently seen in cities, where they are used to construct tall buildings. In a tower crane, a huge metal beam sits atop a vertical metal tower. The beam extends outward from the tower in two directions and it pivots about the top of the tower. A lifting cable hangs from one end of the beam and heavy weights hang from the other end of the beam. Since the lifting cable end of the beam is the only end that seems to do anything, what useful purpose does the weight-end of the beam serve?






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