If the echo (the reflected sound) reaches your ear less than about
0.1 second after the original sound, your brain doesn't separate them,
and you're not aware of the echo even though it's there.
If the echo comes from, say, a wall, 0.1 second means you'd have to be
about 17 meters away from the wall. If you're closer than that, then the
echo reaches you in less than 0.1 second and you're not aware of it.
A. 30 meters . . .
No. You hear that echo easily
B. you're standing within range of both sounds . . .
No. You hear that echo easily, if you're at least 17 meters from the wall.
C. less than 0.1 second later . . .
That's it. The echo is there but your brain doesn't know it.
D. 21.5 meters
No. You hear that echo easily.
The speed of the second satellite is less than the speed of the first satellite.
<h3>What is speed?</h3>
The speed of any moving object is the ratio of the distance covered and the time taken to cover that distance.
Given is a satellite is in a circular orbit around a planet. A second satellite is placed in a different circular orbit that is farther away from the same planet.
When the distance from the center of the orbit increases, the time to complete the orbit will be greater.
Thus, the speed of the second satellite is less than the speed of the first satellite.
Learn more about speed.
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Answer:
Explanation:
The apparent brightness follows an inverse square law, therefore we can write:
where I is the apparent brightness and r is the distance from the Sun.
We can also rewrite the law as
(1)
where in this problem, we have:
apparent brightness at a distance 
, where
million km
We want to estimate the apparent brightness at 
, where is ten times , so
Re-arranging eq.(1), we find 
:
Answer:
False
Explanation:
Let's consider the definition of the angular momentum,
where 
is the moment of inertia for a rigid body. Now, this moment of inertia could change if we change the axis of rotation, because "r" is defined as the distance between the puntual mass and the nearest point on the axis of rotation, but still it's going to have some value. On the other hand,
so 
unless 
║ 
.
In conclusion, a rigid body could rotate about certain axis, generating an angular momentum, but if you choose another axis, there could be some parts of the rigid body rotating around the new axis, especially if there is a projection of the old axis in the new one.
