Answer:
Part a)

Part b)

Explanation:
As we know that electric force on electric charge is given as

here we have

E = 153 N/C
now force is given as

Gravitational force on electric charge near surface of earth is given as


now the ratio of two forces is given as


Part b)
Now the ball is balanced by the electric force and the force of gravity on it
so here we have



here we have

The reversing of the magnet polarity will explain the different current reading.
Answer: Option D
<u>Explanation:</u>
According to Faraday's law of inductance, whenever a bar magnet is moved toward a stationary coil at constant speed, current will be generated in that coil. So in this case, the first maximum current in the above situation say A is recorded successfully.
Similarly, when the arrangement is kept as it is, in situation B, the current is observed to have different reading. This may be because of the polarity of the magnet would have changed leading to different current reading.
Answer:
part (a) 
Part (b) 
Explanation:
Given,
- Mass of the larger disk =

- Mass of the smaller disk =

- Radius of the larger disk =

- Radius of the smaller disk =

- Mass of the block = M = 1.60 kg
Both the disks are welded together, therefore total moment of inertia of the both disks are the summation of the individual moment of inertia of the disks.

part (a)
Given that a block of mass m which is hanging with the smaller disk,
Let 'T' be 'a' be the tension in the string and acceleration of the block.
From the free body diagram of the smaller block,

From the pulley,

From the equation (1) and (2),

part (b)
Above expression for the acceleration of the block is only depended on the radius of the pulley.
Radius of the larger pulley = 
Let
be the acceleration of the block while connecting to the larger pulley.
Answer:
D
Explanation:
F = G m1 m2 / r^2 now double r
F = G m1m1/ (2r)^2
F = 1/4 G m1m2/r^2 <===== this is 1/4 of the original
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