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uysha [10]
3 years ago
10

A rock is dropped from a third story window to the ground below. Assuming air resistance can be ignored, as it falls: a) only it

s kinetic energy is conserved.
b) only its momentum is conserved.
c) both its kinetic energy and its momentum are conserved.
d) only its mechanical energy is conserved.
e) both its mechanical energy and its momentum are conserved.
Physics
1 answer:
aleksklad [387]3 years ago
7 0

Answer:

Option d) only its mechanical energy is conserved

Explanation:

Since, mechanical energy of a system is the sum of its kinetic energy and potential energy.

Potential energy depends directly on height while kinetic energy depend on the speed of the body.

When the rock is dropped its potential energy decreases while its kinetic energy increases while the potential energy is maximum at the top and kinetic energy was zero.

Therefore, these two energies are inter convertible and when one increases the other decreases and vice-versa keeping the overall mechanical energy conserved.

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Answer:

86.4 m  horizontal from landing spot

Explanation:

Find out how long before the ball hits the ground

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find time to hit ground from 100 m  

          ( height will be<u> zero</u> when it hits the ground)

<u>0 </u>=  100  - 2 t  - 1/2 ( 9.81) t^2

        use Quadratic Formula to find t = 4.32 seconds

              horizontal speed of ball = 20 m/s  

in 4.32 seconds it will travel horizontally   20  m/s * 4.32 s = 86.4 m

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Answer:

iv) It is 9x bigger than before

Explanation:

As the amplitudes of the new speakers add directly with the original one, taking into account the phase that they have, the composed amplitude of the sound wave is as follows:

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The intensity of the wave, assuming it propagates evenly in all directions, is constant at a given distance from the source, and can be expressed as follows:

I = P/A

where P= Power of the wave source, A= Area (for a point source, is equal to the surface area of a sphere of radius r, where is r is the distance to the source along a straight line)

For a sinusoidal wave, the power is proportional to the square of the amplitude, so the intensity is proportional to the square of the amplitude also.

If the amplitude changes increasing three times, the change in intensity will be proportional to the square of the change in amplitude, i.e., it will be 9 times bigger.

So, the statement iv) is the right one.

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X rays - These have more short wavelength and can penerate soft tissues like skin & muscle, hence are used for medical examining

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