While John is traveling along a straight interstate highway, he notices that the mile marker reads 249 km. John travels until he
1 answer:
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a)
b)
Explanation:
a)
Since there are no external torques acting on the system, the total angular momentum must remain constant.
At the beginning, the merry-go-round and the girl are at rest, so the initial angular momentum is zero:
Later, after the girl throws the rock, the angular momentum will be:
where:
is the moment of inertia of the merry-go-round
is the moment of inertia of the girl, where
M is the mass of the girl
R is the distance of the girl from the axis of rotation
is the angular speed of the merry-go-round and the girl
is the angular momentum of the rock, where
m is the mass of the rock
v is its velocity
Since the total angular momentum is conserved,
So we find:
And the negative sign indicates that the disk rotates in the direction opposite to the motion of the rock.
b)
The linear speed of a body in rotational motion is given by
where
is the angular speed
r is the distance of the body from the axis of rotation
In this problem, for the girl, we have:
is the angular speed
is the distance of the girl from the axis of rotation
Therefore, her linear speed is:
Answer:
a) 915 m
b) 0.15 W/
Explanation:
solution:
a) The wavelength of the microwaves electromagnetic wave is:
λ==
=0.025 m
the circular radar antenna acts like a circular aperture of diameter D will have a bright central maximum of diameter:
w=2.44λL/D
so at 30 km screen:
w=2.44λL/w
=2.44*0.025*30*10^3/2
=915 m
b)
The area of a beam at 30 km is:
A==
=
=
the average microwave intensity is equal to the ratio of the power of the antenna and area of the beam:
I=P/A
So at 30 km:
I=100*10^3/657*10^3
=0.15 W/