Answer: C. the motion of a spacecraft under gravitational influence.
Explanation:
A is Metallurgy, B is Biology, C is astro-physics, I am not sure what D is, but it's safe to say it's not physics, E, micro-biology, and the study of radiation. C is the only one involving physics.
Answer: 
Explanation:
The <u>centripetal acceleration</u> 
of an object moving in a uniform circular path is given by the following equation:
(1)
Where:
is the tangential velocity
is the radius of the circle
On the other hand, the tangential velocity is expressed as:
(2)
Where 
is the angular velocity, which can be found knowing the child makes 5 revolutions in 13.4s:
(3)
Substituting (3) in (2):
(4)
(5)
Substituting (5) in (1):
(6)
Finally:
C. because energy can not be created or destroyed, but transformed/transferred to maintain equilibrium.
