Answer:
Lifting force, F = 21240 N
Explanation:
It is given that,
Mass of the helicopter, m = 1800 kg
It rises with an upward acceleration of 2 m/s². We need to find the lifting force supplied by its rotating blades. It is given by :
F = mg + ma
Where
mg is its weight
and "ma" is an additional acceleration when it is moving upwards.
So, 
F = 21240 N
So, the lifting force supplied by its rotating blades is 21240 N. Hence, this is the required solution.
Answer:
The following that could be used to make the simplest circuit are a battery, wire, switch, and a light bulb. The answer is letter D. The battery provides the energy for the bulb to work. The wire provides a pathway for the electrons to move. The switch provides the open and close of the circuit.
Explanation:
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Answer:
The amount of work done in order to lift the box is 
Explanation:
Given the weight of each box is 
And the man lifts boxes at a height of 
We need to find the amount of work done.
The amount of work done is the product of applied force
that causes the displacement
.
In our problem force is
and displacement is
.
Now, work done

So, the amount of work done in order to lift the box is 
Answer:
"It will be more than the speed of sound waves in air at 20*C and water at 20*C."
Explanation:
Speed of sound in a medium depends upon the density and elasticity of the medium.
If the elasticity of a medium is greater and the density of that medium is lower, sound will travel faster. Although density is also a factor but the major factor is Elasticity.
Hence, sound travel faster in solids than in liquids and even slower in gases due to elasticity difference.

That is why the speed of sound in glass will be more than the speed of sound waves in air at 20*C and water at 20*C.