Explanation:
the missing figure in the Question has been put in the attachment.
Then from the figure we can observe that
the center of the sphere is positive, therefore, negative charge will be induced at A.
As B is grounded there will not be any charge on B
Hence the answer is A is negative and B is charge less.
Answer:

Explanation:
The two cars are under an uniform linear motion. So, the distance traveled by them is given by:

is the same for both cars when the second one catches up with the first. If we take as reference point the initial position of the second car, we have:

We have
. Thus, solving for t:

Answer:
minimum frequency = 170 Hz
Explanation:
given data
One path long = 20 m
second path long = 21 m
speed of sound = 340 m/s
solution
we get here destructive phase that is path difference of minimum
here λ is the wavelength of the wave
so path difference will be
21 - 20 =
λ = 2 m
and
velocity that is express as
velocity = frequency × wavelength .............1
frequency =
minimum frequency = 170 Hz