First of all, we need to convert the angular speed from rev/min into rev/s:

The angular acceleration is the variation of angular speed divided by the time:

And this is constant, so we can use the following equation to calculate the angle through which the engine has rotated:

so, 5 revolutions.
I do not agree with the statement.
The "substance" can be a compound. It's "pure"
as long as there's nothing else in it but its name.
'Pure' water is 100% H₂O with nothing else in it.
'Pure' table salt is 100% NaCl with nothing else in it.
'Pure' carbon dioxide is 100% CO₂ with nothing else in it.
These example substances are all compounds, not elements.
B Yea that should be the right answer
The motion of the ball on the vertical axis is an accelerated motion, with acceleration

The following relationship holds for an uniformly accelerated motion:

where S is the distance covered, vf the final velocity and vi the initial velocity.
If we take the moment the ball reaches the maximum height (let's call this height h), then at this point of the motion the vertical velocity is zero:

So we can rewrite the equation as

from which we can isolate h

(1)
Now let's assume that

is the initial velocity of the first ball. The second ball has an initial velocity that is twice the one of the first ball:

. So the maximum height of the second ball is

(2)
Which is 4 times the height we found in (1). Therefore, the maximum height of ball 2 is 4 times the maximum height of ball 1.
Answer:

Explanation:
At some distance from the Earth the force of attraction due to moon is balanced by the force due to Moon
so we will have

now we have


so we will have

Now by energy conservation


