How Things Work: An Introduction to Physics week 7

In this blog you will find the correct answer of the Coursera quiz How Things Work: An Introduction to Physics week 7 mixsaver always try to brings best blogs and best coupon codes

Week- 7

Bumper Cars

1. A meteor is streaking toward city hall and will hit the building in a few second. As it moves through the sky, what physical quantities is the meteor carrying with it? [Ignore any effects due to air or Earth’s gravity]

Energy, momentum directed toward city hall, but no force.
Energy, momentum directed toward city hall, and an enormous force directed toward city hall.
Energy, an enormous force directed toward city hall, but no momentum.
Energy, but no momentum and no force.

2. You have a midnight craving for ice cream and are walking quickly through your pitch-black apartment when you collide with the wall. You come to a complete stop. Fortunately, your interior decorator mounted a thick woolen tapestry (wall-hanging) on the concrete wall and that soft tapestry saves you from injury. Compare the momentum you transferred while coming to a stop on the tapestry-covered wall to the momentum you would have transferred if you had come to a stop on the bare concrete wall.

You would have transferred the same momentum in either case, but in stopping on the tapestry-covered wall you transferred that momentum with a larger force over a shorter period of time.
You transferred more momentum while stopping on the tapestry-covered wall than you would have transferred while stopping on the bare wall.
You transferred less momentum while stopping on the tapestry-covered wall than you would have transferred while stopping on the bare wall.
You would have transferred the same momentum in either case, but in stopping on the tapestry-covered wall you transferred that momentum with a smaller force over a longer period of time.

3. A car traveling at 60 mph (100 km/h) veers off the road and hits a tree. The car immediately comes to a complete stop. Fortunately, the airbag inflates and the driver comes to a stop in the airbag instead of coming to a stop on the steering wheel. Hitting the airbag rather than the steering wheel saves the driver’s life because the driver

carries less force with her before colliding with the airbag than she would have carried with her if there were no airbag.
transfers more momentum to the airbag than she would have transferred to the steering wheel.
transfers all of her momentum to whatever stops her, but that transfer is slower and involves a smaller force when she hits the airbag.
transfers less momentum to the airbag than she would have transferred to the steering wheel.

4. A diver stands upright at the edge of the 10 meter platform at the Olympics. The diver jumps off the platform, folds into a ball shape, completes 3.5 somersaults, unfold out of the ball shape, and plunges head-first into the water. Compare the diver’s angular momentum about the diver’s center of mass at three different moments while that diver is not touching anything: (a) before folding into a ball shape, (b) while ball-shaped, and (c) after unfolding out of the ball shape [Note that the diver’s weight, which acts at the diver’s center of gravity, produces zero torque on the diver about the diver’s center of mass. Ignore any effects due to the air.]

The diver’s angular momentum is greatest at moment (b), as the diver is completing somersaults.
The diver’s angular momentum is the same at all three moments.
The diver’s angular momentum is greatest at moment (a), before the diver folds into a ball shape.
The diver’s angular momentum is greatest at moment (c), after the diver unfolds out of the ball shape.

5. The chef at a pizza restaurant tosses a spinning disk of pizza dough into the air. As the disk stretches outward in midair and its diameter increases, what happens to the disk’s angular momentum and angular velocity about the disk’s center of mass? [Note that the disk’s weight, which acts at the disk’s center of gravity, produces zero torque on the disk about the disk’s center of mass. Ignore any effects due to the air.]

The disk’s angular velocity is constant, but the disk’s angular momentum increases.
The disk’s angular momentum is constant, but the disk’s angular velocity increases.
The disk’s angular momentum is constant, but the disk’s angular velocity decreases.
The disk’s angular momentum and angular velocity are both constant.

6. You are riding on a large carousel at an amusement park and you are enjoying the moving scenery as the carousel spins about its center of rotation. The ride comes to an end and the carousel gradually slows to a stop. Why does it take so long for the carousel to stop rotating?

The spinning carousel carries a large amount of angular momentum and the angular impulse needed to remove that angular momentum with a reasonable torque requires a long time.
The spinning carousel has a large angular velocity and changing a large angular velocity requires a long time.
The spinning carousel has a large rotational mass and changing a large rotational mass requires a long time.
The spinning carousel has a large angular impulse and changing a large angular impulse requires a long time.

7. A “lazy susan” is a disk-shaped rotating platform that a restaurant places at the center of a large dining table. Dishes of food are placed on the lazy susan and diners can rotate the lazy susan by hand to bring various dishes closer to them. A large torque exerted for a short time makes the motionless platform begin rotating rapidly, but that dangerous technique risks tipping over some of the food dishes. How can you make the same motionless platform and dishes begin rotating just as rapidly, but with a smaller, safer torque?

Do the same angular impulse as the dangerous technique, but by exerting a smaller torque for a smaller time.
Do the same angular impulse as the dangerous technique, but by exerting the smaller torque for a larger rotational mass.
Do the same angular impulse as the dangerous technique, but by exerting the smaller torque for a smaller rotational mass.
Do the same angular impulse as the dangerous technique, but by exerting a smaller torque for a longer time.

8. To win a big prize at the fair or festival, all you have to do is toss a basketball into a bucket located about 10 feet (3 meters) in front of you and have the basketball remain in the bucket. The rigid bucket cannot move and it opens toward you. However, the bucket is tilted upward just enough that the basketball will remain in it if someone places the basketball in the bucket by hand. You try a dozen times to get the basketball to stay in the bucket, but it keeps bouncing back out of the bucket. Why is it so difficult for the basketball to come to rest in the bucket?

To stop moving, the basketball must transfer both energy and momentum to the bucket and, while it transfers momentum easily to the bucket, it transfers almost zero energy to the bucket.
To stop moving, the basketball must transfer both energy and momentum to the bucket and, while it transfers energy easily to the bucket, it transfers almost zero momentum to the bucket.
To stop moving, the basketball must transfer both energy and momentum to the bucket and it transfers almost zero energy and almost zero momentum to the bucket.
To stop moving, the basketball must transform its energy into momentum. During its impact with the bucket, there is not enough time to complete that transformation.

9. You have just added a massive stone sculpture to your modern art collection. Unfortunately, the people who delivered the sculpture accidentally set it on its side. What barbarians! To tip the sculpture onto its proper base, you transfer as much momentum as you can to the highest point on the sculpture. You accomplish this transfer (successfully, I might add) by running full speed toward the sculpture and

hitting the highest point on the sculpture with the softest part of your body so that you come to a complete stop.
hitting the highest point on the sculpture with the hardest part of your body so that you come to a complete stop.
hitting the highest point on the sculpture with your feet as you jump against it so that you end up reversing your velocity.
continuing past the sculpture without touching it (you evidently lost your nerve).

10. Your dynamic sculpture combines magnets, springs, and elastic bands with a variety of moving parts, including levers, pulleys, and pendulums. When someone jostles those parts, a complicated series of motions occurs and predicting how things will proceed seems nearly impossible. You point out, however, that there is a simple rule governing the motion of each part at any moment in time. That rule is that each part

continues in motion at constant velocity.
moves when it experiences a net force and stops when the net force on it is zero.
has constant energy, momentum, and angular momentum.
accelerates in the direction that reduces its total potential energy as quickly as possible.

Important Links: