If the object is moving in a straight line at a constant speed, then that's
the definition of zero acceleration. It can only happen when the sum of
all forces (the 'net' force) on the object is zero.
And it doesn't matter what the object's mass is. That argument is true
for specks of dust, battleships, rocks, stars, rock-stars, planets, and
everything in between.
a) It is absolute, so it does not change.
b) Inertial ones.
c) Inside the train the time will slow down relatively to the outside clock. So if one travel at nearly the speed if light for 2 hours on his clock, for outdoor observers it will look like 3 hours.
Explanation:
(1). Formula to calculate the potential difference is as follows.
= 
= 
= 
= 
= 38.7 volts
Therefore, magnitude of the potential difference between the two spheres is 38.7 volts.
(2). Now, formula to calculate the energy stored in the capacitor is as follows.
E = 
= 
= 
Thus, the electric-field energy stored in the capacitor is
.
Answer:

Explanation:
From the attached file diagram, the total force acting on the charged box is the downward weight and the repulsive force acting in opposite to the weight force . Hence we can write the total force as

When fixed,F=o
Hence

The value of the acceleration is 16.2m/s^2
Answer:
Speed=1.6km/hr. I'm not sure about b