The answer to ur question is: B
Answer:
Part a)

Part b)

Explanation:
Part a)
Angular speed of the pedal is changing from 60 rpm to 90 rpm in 10 s
so the angular acceleration is given as

so we will have


now the tangential acceleration of the pedal is given as



Part b)
Total angular displacement made by the sprocket in the interval of 10 s is given as



now length of the chain passing over it is given as



6 months with no sunrise and the other 6 without a sunset, at some places on Earth, are the result of the orientation of Earth's axis.
First of all, the question is worded somewhat ambiguously because mass does not necessarily imply that there is a force (i.e. an object could be stationary in a system with no gravity and not have a force, or something of the like). Moreover, simply because an object is twice the mass does not mean the force will change.
However, we know from Newton's second law that F = ma. Therefore, force will increase or decrease proportionally with mass. This means if an object maintains a contestant acceleration and its mass doubles, the force that it provides will also double.
Perimeter = 2 ( L + W )
32 = 2 ( L + W )
16 = L + W
L = 16 - W
Area = L W
63 = L W
63 = (16-W) W
63 = 16W - W²
-W² + 16 W - 63 = 0
By factorizing W = 9 or W = 7
So the dimensions are 7 and 9