Which of the following does not use electromagnetic radiation? (Check all that apply)
1 answer:
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Answer:
h = 3.3 m (Look at the explanation below, please)
Explanation:
This question has to do with kinetic and potential energy. At the beginning (time of launch), there is no potential energy- we assume it starts from the ground. There, is, however, kinetic energy
Kinetic energy = m
Plug in the numbers = (4.0)(
)
Solve = 2(64) = 128 J
Now, since we know that the mechanical energy of a system always remains constant in the absence of outside forces (there is no outside force here), we can deduce that the kinetic energy at the bottom is equal to the potential energy at the top. Look at the diagram I have attached.
Potential energy = mgh = (4.0)(9.8)(h) = 39.2(h)
Kinetic energy = Potential Energy
128 J = 39.2h
h = 3.26 m
h= 3.3 m (because of significant figures)
(a)
The total mechanical energy of the projectile at the beginning is the sum of the initial kinetic energy (K) and potential energy (U):
The initial kinetic energy is:
where m = 58.0 kg is the mass of the projectile and is the initial speed. Substituting,
The initial potential energy is given by
where g=9.8 m/s^2 is the gravitational acceleration and h=132 m is the height of the cliff. Substituting,
So, the initial mechanical energy is
(b)
We need to calculate the total mechanical energy of the projectile when it reaches its maximum height of y=336 m, where it is travelling at a speed of v=99.2 m/s.
The kinetic energy is
while the potential energy is
So, the mechanical energy is
And the work done by friction is equal to the difference between the initial mechanical energy of the projectile, and the new mechanical energy:
And the work is negative because air friction is opposite to the direction of motion of the projectile.
(c) 88.1 m/s
The work done by air friction when the projectile goes down is one and a half times (which means 1.5 times) the work done when it is going up, so:
When the projectile hits the ground, its potential energy is zero, because the heigth is zero: h=0, U=0. So, the projectile has only kinetic energy:
E = K
The final mechanical energy of the projectile will be the mechanical energy at the point of maximum height plus the work done by friction:
And this is only kinetic energy:
So, we can solve to find the final speed: