Answer: In the case of gravity, mediated by spin 2 particles, charge is mass, which is always positive. Thus, q1q2 is always greater than zero, and gravity is always attractive. For spin 0 force mediators, however, there is no restriction on the charges and you can very well have repulsive forces.
Explanation: C) both an attractive and repulsive force is the answer
centripetal acceleration is given by formula

given that


now we have




so the ratationa frequency is given by




(since you asked for basic understanding only, I am not including actual calculations. Please let me know in the comments section if you wish to verify your solution(s))
For (b): Use the formula for distance (s) made during an accelerated motion:

with v_0 and s_0 being the initial velocity and distance, both 0 in this case, and with "a" denoting the acceleration, in this case solely due to gravitational acceleration so: "g."
You are given the distance made, namely 10 m, and the duration t (0.88s) and so using the formula above you can solve for g.
For (c), to determine the final velocity at time 0.88s use the formula for the instantaneous velocity of an accelerated motion
(velocity at time t) = (acceleration) x (time)
again, with acceleration due to gravity, i.e., a = g and with g as determined under (b).
If my calculation is correct, this mystery planet could be the Jupiter.
The answer 1 is
The best-known use of radio waves is for communication; television, cellphones and radios all receive radio waves and convert them to mechanical vibrations in the speaker to create sound waves that can be heard.Electromagnetic radiation is transmitted inwaves or particles at different wavelengths and frequencies.
the answer 2 is
Radio Waves: Instant Communication
Microwaves: Data and Heat
i think the answer number 3 is
It is all about wavelength versus tunnel diameter. The wavelength of GPS is about 20cm it would happily propagate in any normal tunnel if it could get in but the earth and other structures absorb it. AM radio (600kHz - 1500kHz) cannot propagate in any normal tunnel because the wavelength is too long (500m-200m) relative to the diameter, and thus gets reflected at the entrance. FM (100MHz ~ 3m) would propagate and it does for a while but then it suffers reflections