Answer:
The work done by gravity is 784 J.
Explanation:
Given:
Mass of the block is, 
Height to which it is raised is, 
Acceleration due to gravity is, 
Now, work done by gravity is equal to the product of force of gravity and the distance moved in the direction of gravity. So,

Force of gravity is given as the product of mass and acceleration due to gravity.
. Now,

Therefore, the work done by gravity is 784 J.
<h2>The man have to apply force of 160 N</h2>
Explanation:
The work done to lift the bag of weight mg through height 2.5 m is 400 J
The work done can be found by relation W = mg x h
Thus mg =
=
= 160 N
Therefore the man have to apply the force of 160 N
Answer:
Power of the string wave will be equal to 5.464 watt
Explanation:
We have given mass per unit length is 0.050 kg/m
Tension in the string T = 60 N
Amplitude of the wave A = 5 cm = 0.05 m
Frequency f = 8 Hz
So angular frequency 
Velocity of the string wave is equal to 
Power of wave propagation is equal to 
So power of the wave will be equal to 5.464 watt
That's a molecule of the substance. You can break the molecule down further, into the atoms that make it up, but those don't have the properties of the original 'compound'.
Here's an example:
-- Sodium is a soft, slippery metal, that explodes when water touches it.
-- Chlorine is a poisonous green gas.
When an atom of Sodium and an atom of Chlorine combine, they make one molecule of a substance called "Sodium Chloride". That's SALT ! It isn't green, it isn't a gas, it isn't poisonous, it isn't soft and slippery, and it doesn't explode when water touches it.