# Physics (3: Gravity, Force, & Space)

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Multiple Choice Questions (33)

air resistance

### Balloons rise until

the surrounding air becomes too dense

### At an altitude of 220 km, the downward force of gravity on an Earth satellite is

a little bit weaker

### Airplanes fly (maintain their altitude) by

pushing air downward

### Rockets fly by

pushing burned fuel downward

the low pressure

### When an astronaut in space sneezes, his head is snapped back with higher velocity on Earth, because

Wrong! His head is not snapped back with higher velocity

### A rail gun

doesn't really accelerate things

2 miles

### The method that would take the least energy to get something to space is

lifting it by an elevator (f the elevator existed)

1 month

1 day

### The force of gravity between two people standing next to each other is

small but measurable (flea/10^-7)

### You can see where the tropopause is by

looking at the tops of thunderstroms

### If satellites fly too low, they will crash because

of stronger gravity

### Ice-skaters spin faster by pulling in their arms. This illustrates that

angular momentum is conserved

### Someone firing a rifle is pushed back by the rifle. This illustrates that

momentum is conserved

### A problem with rail guns is that

the high accelerations can cause damage

3 g's

### The lowest practical altitude for a satellite orbiting the Earth is about

600 miles (a few hundred)

ion rocket

22,000 miles

### Skyhook, if built, is

a way to get into space using less energy

22 mph

### Artificial gravity can be created in a spaceship by

accelerating the ship

5 miles/second

### The Sun is mostly hydrogen, yet the Earth has very little hydrogen gas. That's because

it escaped to space

### The orbit of GPS is

MEO (Medium Earth Orbit)

### A geosynchronous satellite orbits the Earth

once every 24 hours

one minute

### Compared to the weight of the payload, the fuel used in a rocket to orbit typically weighs

over 20 times more

### Spy satellite usually fly at

LEO (Low Earth Orbit)

Example: