Answer:
D. ) The force would be zero newtons
Explanation:
Because
If you are at the center of the earth, gravity is zero because all the mass around you is pulling "up" (every direction there is up!)
So F=mg so if g is zero F is also zero
Answer:

Explanation:
assume
M= mass of Mars
m=mass of phobos
r=orbital radius
T=period
we can apply F=ma to this orbital motion (considering the cricular motion laws)
where,
and a=rω^2
where ω=
and G is the universal gravitational constant.
G = 6.67 x 10-11 N m2 / kg2

1). both
2). Venus
3). Venus catastrophically; Earth too but much less.
4). Earth
5). Earth
6). Venus (It would be pretty hard for US to mistake Earth for a star.)
Answer:
The minimum riding speed relative to the whistle (stationary) to be able to hear the sound at 21.0 kHz frequency is 15.7 m/s
Explanation:
The Doppler shift equation is given as follows;

Where:
f' = Required observed frequency = 20.0 kHz
f = Real frequency = 21.0 kHz
v = Sound wave velocity = 330 m/s
= Observer velocity = X m/s
= Source velocity = 0 m/s (Assuming the source is stationary)
Which gives;

330 -
= (20/21)*330
= 330 - (20/21)*330 = 15.7 m/s
The minimum riding speed relative to the whistle (stationary) to be able to hear the sound at 21.0 kHz frequency = 15.7 m/s.