Anonymous
Anonymous asked in 科學及數學其他 - 科學 · 1 decade ago

# Physics questions

a point on a string vibrating as a sine wave is just at its extreme position. If it takes 2s for it to move to the other extreme position, what is the period of the wave?

a screw jack is used to raise a 900N load. If the efficiency is 90% and 5% of the input energy is used to overcome friction, what is the weight of the moving parts?

what is the use of stroboscope?

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Q:a point on a string vibrating as a sine wave is just at its extreme position. If it takes 2s for it to move to the other extreme position, what is the period of the wave?

A: The period is the time taken for the same particle (or point) to move from one extreme position to the other and back.

Thus, the period = 2 x 2s = 4s

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Q: a screw jack is used to raise a 900N load. If the efficiency is 90% and 5% of the input energy is used to overcome friction, what is the weight of the moving parts?

A: Since efficiency is 90%, i.e. 10% of input energy is wasted in doing work against friction and in raising the moving part.

Thus percentage of input energy in raising moving part = (10-5)% = 5%

The weight of moving part = [900/0.9 x 0.05] N = 40.5 N

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Q: what is the use of stroboscope?

A: A stroboscope is used to measure the speed of rotation, or frequency of vibration of a mechanical part of system. It can also be used to measure the speed of accelration of a fast moving object.

It works by illuminating an object with brilliant flashes of light (or using intermittent shutter) such that the moving object is seen stationary.

You may refer to the following web-page:

• Anonymous

1. a point on a string vibrating as a sine wave is just at its extreme position. If it takes 2s for it to move to the other extreme position, what is the period of the wave?

-- &gt; 2s

2. a screw jack is used to raise a 900N load. If the efficiency is 90% and 5% of the input energy is used to overcome friction, what is the weight of the moving parts?

唔知咩係screw jack...

3. what is the use of stroboscope?

To find out the frequency of wave

Source(s): myself