In a direct current, the electric charge, or current, only flows in one direction. In an alternating current, the electric charge changes periodically.
Violet light is at the end of the visible light section of the electromagnetic spectrum. Ultraviolet rays are directly next to violet rays on the EM Spectrum.
Answer:
Weight = 4900 N
Explanation:
Given:
Mass of the piano is, 
Acceleration due to gravity is, 
Height to which the piano is raised is 8.0 m.
We are asked to determine the weight of the piano.
We know that, weight of a body is nothing but gravitational force acting on it by the center of Earth. It is equal to the product of mass and acceleration due to gravity.
Weight is independent of height til the height is very less than the radius of Earth. At very high altitudes which are comparable to the radius of Earth, the value of 'g' changes and hence the weight. But, here the height is very small and hence the value of 'g' equals 9.8 m/s² only.
Thus, weight of the piano is given as:
Weight = Mass
Acceleration due to gravity
Weight = 
Weight = 
Weight is a force so, its unit is same as that of force and hence it is measured in Newtons.
Therefore, the weight of the piano is 4900 N.
Potential energy = mgh
So, energy gained
= mgh
= 70kg × (9.8m/s²) × 1000m
= 686000 kgm²/s²
= 686000 J