Answer: D. Hydroelectric power
Explanation: Hydroelectric means water power (not exactly but "hydro" is water and electric is well self explanatory)
g Generally the accepted value of acceleration due to gravity is 9.801 
as per the question the acceleration due to gravity is found to be 9.42
in an experiment performed.
the difference between the ideal and observed value is 0.381.
hence the error is -
=3.88735 percent
the error is not so high,so it can be accepted.
now we have to know why this occurs-the equation of time period of the simple pendulum is give as-![T=2\pi\sqrt[2]{l/g}](https://tex.z-dn.net/?f=T%3D2%5Cpi%5Csqrt%5B2%5D%7Bl%2Fg%7D)

As the experiment is done under air resistance,so it will affect to the time period.hence the time period will be more which in turn decreases the value of g.
if this experiment is done in a environment of zero air resistance,we will get the value of g which must be approximately equal to 9.801 
Amalgamating is the coating of zinc plate with mercury.
Yes, it is <span>accurate to describe the physical universe as composed of only matter and energy. Some people might argue about the dark matter, but it is not yet defined properly. Different universes can be made up of different compositions but it is a fact that our universe is made of matter and energy. </span>
Answer:
a) Θ = ω₀*t + ½αt² To complete first revolution 2π rads = 0*t + ½αt² and to complete the first and second combined 4π rads = 0*t + ½α(t+0.810s)² Divide second by first: 2 = (t + 0.810s)² / t² This is quadratic in t and has roots at t = -0.336 s ← ignore and t = 1.96 s ◄ b) Use either equation from above: 2π rads = 0*t + ½α(1.96s)² α = 3.27 rad/s² ◄ Hope this helps!
Explanation: