Conduction. Any material that easily allows heat to move through it. Vacuum. A region of space that contains no matter. Solid.
No one can answer that kind of question since it was a specific project.
Answer:
a). Determine the magnitude of the gravitational force exerted on each by the earth.
Rock: 
Pebble: 
(b)Calculate the magnitude of the acceleration of each object when released.
Rock: 
Pebble: 
Explanation:
The universal law of gravitation is defined as:
(1)
Where G is the gravitational constant, m1 and m2 are the masses of the two objects and r is the distance between them.
<em>Case for the rock </em>
<em>:</em>
m1 will be equal to the mass of the Earth
and since the rock and the pebble are held near the surface of the Earth, then, r will be equal to the radius of the Earth
.

Newton's second law can be used to know the acceleration.

(2)

<em>Case for the pebble </em>
<em>:</em>


Answer:
648.40N
Explanation:
Centripetal acceleration is the acceleration of an object around a circular path. Centripetal for e acting on the combined mass is expressed as:
F = ma
F = mv²/r
m is the mass of the object = 143kg
v is the linear velocity = 13.8m/s
r is the radius = 42.0m
Substitute the given parameters into the formula;
F = 143*13.8²/42
F = 27,232.92/42
F = 648.40N
Hence the magnitude of the centripetal force acting on the combined mass is 648.40N