Answers:
a) 5400000 J
b) 45.92 m
Explanation:
a) The kinetic energy 
of an object is given by:
Where:
is the mass of the train
is the speed of the train
Solving the equation:
This is the train's kinetic energy at its top speed
b) Now, according to the Conservation of Energy Law, the total initial energy is equal to the total final energy:
Where:
is the train's initial kinetic energy
is the train's initial potential energy
is the train's final kinetic energy
is the train's final potential energy, where 
is the acceleration due gravity and 
is the height.
Rewriting the equation with the given values:
Finding :
If you're moving, then you have kinetic energy.
If you're not at the bottom yet, then you still have
some potential energy left.
The FREQUENCY of light remains unchanged once it leaves the source.
Answer:
Explanation: Weight of space probes on earth is given by:
W= weight of the object( in N)
m= mass of the object (in kg)
g=acceleration due to gravity(9.81 
)
Therefore,
Similarly,
Now, considering these two parts as uniform spherical objects
Also, according to Superposition principle, gravitational net force experienced by an object is sum of all individual forces on the object.
Force between these two objects is given by:
G= gravitational constant (
)
= masses of the object
R= distance between their centres (in m)(18 m)
Substituiting all these values into the above formula
This is the magnitude of force experienced by each part in the direction towards the other part, i.e the gravitational force is attractive in nature.
