Explanation

The main idea of the solar system was proposed by the Polish astronomer Nicolaus Copernicus (1473-1543).

who said that "the Sun is the centre of the Universe" and made the planets move around it in perfect circles

(in his book entitled, "On the Revolution of the Celestial Spheres", written in Latin and published in 1543)

Explanation

Railway tracks are made of steel, which expands in summer heat.

The gaps between rails allow space for this expansion, preventing the tracks from buckling or derailing trains.

Explanation

A kilowatt-hour (unit symbol: kW⋅h or kW h; commonly written as kWh) is a non-SI unit of energy

equal to 3.6 megajoules (MJ) in SI units

.Kilowatt-hours are a common billing unit for electrical energy supplied by electric utilities.

Explanation

Explanation

The ball shares the train’s horizontal velocity, so it moves forward with the train.

As a result, it comes back down into the thrower’s hand.