Answer:
A simple machine consisting of an axle to which a wheel is fastened so that torque applied to the wheel winds a rope or chain onto the axle, yielding a mechanical advantage equal to the ratio of the diameter of the wheel to that of the axle.
Answer:
The correct option is (c).
Explanation:
Given that,
The energy of a photon is, 
We need to tell the color of this light. We know that, the energy of a photon is given by :

Where
c is the speed of light

The wavelength of yellow light is approx 580 nm. Hence, we can say that this photon corresponds to yellow light.
Answer:

Explanation:
Given data

To find
Magnitude of the net magnetic field B
Solution
The magnitude of the net magnetic field can be find as:

I would say that this is the first law of thermodynamics.
Answer:
The correct answer is option B. coal
Explanation:
Coal is made of remains of organic material including trees and other vegetation which got trapped beneath the earth’s surface or at the bottom of the swamps. After burial below the ground the organic material was acted upon by the high temperature and pressure in the absence of air to form peat. Peat after further processing for a longer period of time converted into coal