Correct one is b
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Answer: The correct answer is "magnetic field".
Explanation:
A magnetic field is produced around the current carrying wire.
If you bring compass needle around the current carrying wire then it shows the deflection which indicates that there is a magnetic field around the current carrying wire.
Magnetic fields are the area around the surrounding of magnet in which magnetic force can be experienced.
Therefore, a magnetic field is produced around a wire when an electrical current is in the wire.
If l and m both are doubled then the period becomes √2*T
what is a simple pendulum?
It is the one which can be considered to be a point mass suspended from a string or rod of negligible mass.
A pendulum is a weight suspended from a pivot so that it can swing freely.
Here,
A certain frictionless simple pendulum having a length l and mass m
mass of pendulum = m
length of the pendulum = l
The period of simple pendulum is:

Where k is the constant.
Now the length and mass are doubled,
m' = 2m
l' = 2l



Hence,
If l and m both are doubled then the period becomes √2*T
Learn more about Simple Harmonic Motion here:
<u>brainly.com/question/17315536</u>
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given,
mass of bicyclist(m)=90Kg
centripetal acceleration(a)=1.5 m/s2
centripetal force(F)=ma= 90×1.5=145 N