Answer:
Part a)

Part b)

Part c)

Part d)
from t = 0 to t = 4.9 s
so the reading of the scale will be same as that of weight of the block
Then its speed will reduce to zero in next 3.2 s
from t = 4.9 to t = 8.1 s
The reading of the scale will be less than the actual mass
Explanation:
Part a)
When elevator is ascending with constant speed then we will have



So it will read same as that of the mass

Part b)
When elevator is decending with constant speed then we will have



So it will read same as that of the mass

Part c)
When elevator is ascending with constant speed 39 m/s and acceleration 10 m/s/s then we will have



Reading is given as



Part d)
Here the speed of the elevator is constant initially
from t = 0 to t = 4.9 s
so the reading of the scale will be same as that of weight of the block
Then its speed will reduce to zero in next 3.2 s
from t = 4.9 to t = 8.1 s
The reading of the scale will be less than the actual mass
The ball rolls horizontally thus it is not affected by the gravitational acceleration. We assume that velocity is constant since we are not given acceleration. Therefore, acceleration is zero. The speed of the ball after 2 seconds will still be the same given we have a constant velocity system. Option A is the answer.
Answer:
b) in a direction that makes its potential energy decrease.
Explanation:
- As the electric field has the direction that would take a positive test charge under its sole influence, the positive test charge, will have an increase in its kinetic energy.
- Due to the conservation of energy, in absence of non-conservative forces, this increment must be equal and opposite to the change in electric potential energy, which will be always negative, independent of the sign of the charge.

Therefore, the ball has a velocity of 4m/s.