1. You find a half-sunken barge which is full of compressed helium gas cylinders

Question

1. You find a half-sunken barge which is full of compressed helium gas cylinders which you empty out. To have some fun, you get one of the full helium gas cylinders and put it on top of a dolly (a wheeled platform). You sit behind the gas cylinder and point the opening of the cylinder in the backward direction. When you open the valve on the gas cylinder the helium gas goes rushing out with a loud roar! The dolly accelerates rapidly in the forward direction. To see a similar (but MUCH more dangerous!) situation, look here: http://www.youtube.com/watch?v=ejEJGNLTo84 This happens because

A. The stream of helium gas hits a wall and pushes off it, forcing the dolly forward

B. The mass of the cylinder becomes less, forcing the dolly in the forward direction

C. as the mass of helium moves in the reverse direction, the dolly recoils in the forward direction.

D. a vacuum forms near the nozzle. When the air rushes back in (nature abhors a vacuum) it pushes the dolly in the forward direction.

2.Someone donates a brand new satellite dish for the house.  You install a Satellite dish on the house so they can get 150 channels.  To align the satellite dish you point it to the south at a particular angle to the horizon.  You look at the TV signal as you align it and find that even tiny angular adjustments will cause you to lose the signal.  There is one particular point in the sky where the satellite dish can point and the TV reception is excellent during the day time or at night. The reason this is the case is:

There is a broadcast station which is located in the kuiper belt which beams transmissions exactly to your house.

There is a broadcast station located at the equator which bounces signals off the troposphere which you receive.

There is a geosynchronous satellite which is fixed over the equator at a particular point.  The satellite dish is aimed toward that point.

There is a series of geosynchronous satellites which constantly appear at that point in the sky, each one appearing for several hours before being replaced by another satellite

3. Most of us don't get to experience truly extreme accelerations. An exception are navy pilots who must take off and land on aircraft carriers. To see what it is like to takeoff from an aircraft carrier see here:  http://www.youtube.com/watch?v=TocY6N5thtQ

At the end you see a woman pilot experience her first shot off a carrier. Here is a male pilot's first shot:

http://www.youtube.com/watch?v=fYHDy81QO2Y

Pretty intense isn't it? 0 to 180 mph in 200 ft, corresponds to 0 to 80 m/s in 61 meters or approximately 5 g's of acceleration (52 m/s^2).

During the shot the pilot feels herself pushed back into her seat with an enormous force. What direction is the NET force on her?

In the rear direction.

In the up direction.

In the forward direction.

There is no way to tell.

There is a broadcast station which is located in the kuiper belt which beams transmissions exactly to your house.

There is a broadcast station located at the equator which bounces signals off the troposphere which you receive.

There is a geosynchronous satellite which is fixed over the equator at a particular point.  The satellite dish is aimed toward that point.

There is a series of geosynchronous satellites which constantly appear at that point in the sky, each one appearing for several hours before being replaced by another satellite

Explanation / Answer

1)    D) . A vacuum forms near the nozzle. When the air rushes back in (nature abhors a vacuum) it pushes the dolly in the forward direction.

2)    D) There is a series of geosynchronous satellites which constantly appear at that point in the sky, each one appearing for several hours before being replaced by another satellite

3)    direction is the NET force on her   =    In the rear direction.

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