Physics and mechanical vibration questions in the first year of high school, and physical and mechan

The amplitude is 5cm, the period, this can be answered directly, the frequency f=1 t=, t=, so the amplitude of a period is 5cm (a cycle has walked through four amplitudes), the oscillator has a positive displacement of 5cm to a negative displacement of -5cm, so the displacement is -5cm (the equilibrium position is the displacement of zero), the maximum acceleration in the negative displacement is positive, the velocity is 0, and the acceleration motion is done.

Solution: When the swing ball reaches its lowest point.

1/2mv^2=mgl(1-cosθ)

MV 2 l = t-mg (t is the rope tension).

Therefore t=mg(3-2cos)=

The answer is obviously questionable, the dangling pull force must be greater than the gravity force in order to provide the centripetal force.

And gravity already has. Do you take a look at it again?

Tell you how.

You do it with the conservation of energy.

Suppose the potential energy of the swing ball is zero at the lowest point.

Since there is no initial velocity, all the potential energy of the initial position is converted into kinetic energy at the lowest point.

The potential energy at the initial point can be obtained from the known pendulum length, mass, and angle.

And because the velocity at the lowest point is perpendicular to the pendulum rope, and the resultant force is along the direction of the rope, the centripetal force can be obtained by using the method of finding the centripetal force.

Don't forget, gravity works.

I know, I just can't write it with a computer's keyboard. Suffering.

A:, that is to say, when the train is running at a speed of 40m s, it will vibrate every time, which coincides with the natural vibration cycle of the train and is prone to resonance, so it is a dangerous speed.

B: The need to slow down across the bridge is to prevent the bridge from resonating and breaking, not to prevent the train from resonating, the train will resonate at 40m s, which is the whole process needs to be paid attention to, not just the bridge.

C: The speed of the train should be less than the dangerous speed when running, otherwise danger will occur. The dangerous speed is the length of the rail divided by the natural vibration period of the train, and the length of the rail can only be increased to increase the speed of the train under the condition that the natural vibration period remains unchanged.

v=, i.e., this speed is dangerous, because when the train moves at this speed, the vibration frequency of the rail is equal to the natural frequency of the train, causing resonance. A right.

v = s t, when increasing the rail length s, v can be increased, c pair.

If the speed of the train is higher than 40m s, the deceleration of the train crossing the bridge will make the vibration frequency of the rail equal to the natural frequency of the train, causing resonance and B error.

In T time, a bell vibrates 1 t1 * t times, and b clock vibrates 1 t2 * t times, because a, b, two bells in t time a fast and a slow t time, the number of accurate pendulum clock vibrations in 2t time should be equal to the number of vibrations of a and b each walk t time, that is, 1 t1 * t + 1 t2 * t = 2 * 1 t * t * t that is, t t1 + t t2 = 2. 1) Because the clock corresponding to t in the answer is accurate, the exact clock time t is equal to the real time t, i.e., t t=1, and equation (1) is the same as the answer.

First of all, the timing method of the pendulum clock is clarified: that is, the multiple of the time (period) to complete a full vibration.

The physical meaning of t t refers to the number of times a single pendulum completes full vibration in t time.

So the meaning of the formula should mean:

In the real time t, the number of full vibrations completed by pendulum clock A is equal to the number of full vibrations completed by pendulum clock b.

That is, the pendulum clock a mentioned in the title is faster t(s) in a certain period of time, and the pendulum clock b is slower t(s),) in the same period of time

1.If you don't see the graph, you should use Newton's second law f-mg=ma and choose a positive direction (up).

You can find it. 2.By the formula t=2 (l g)Compute.

From the formula, it can be seen that in the case of a fixed pendulum length, where the gravitational acceleration is large, the period of single pendulum vibration should be smaller. Therefore, the period of vibration in Beijing should be smaller, so the time in Beijing is fast.

The pendulum length l is calculated by substituting the formula of t1 = 1 second and the gravitational acceleration g1 = of Shanghai into the periodic formula, and then using the gravitational acceleration g2 = substituting the periodic formula of Beijing to calculate t2, which is 31 seconds faster by multiplying the time of the previous day and night by 24 hours x 3600 seconds.

。It is perpendicular to the direction of vibration and propagation, which is a transverse wave. The direction of vibration is parallel to the direction of propagation, which is a longitudinal wave.

The direction of vibration alone cannot be determined.

3.Wrong. The distance between the two mistresses that should be adjacent is the wavelength.

4.That's right. Because according to the characteristics of the simple harmonic sin function, the displacements of two points half a wavelength apart are equally opposite. i.e. equal in size.

The equivalent pendulum length of a single pendulum l=lsin

The period of a single pendulum t=2 root number lsin g

The fall time of the ball b = 2h g

The condition for the B ball to hit the A ball is that the fall time of the B ball is an integer multiple of the half-cycle of the A ball, i.e., t=nt 2h=n 2 2lsin 2

As you can see from the graph, the waveform has shifted by a quarter of a wavelength and the wavelength is 24cm, so: 24cm (1 4) = 6cm

It's not very clear, I'll ask later.

The period is: t=1

4×4cm×

So: the magnitude of the displacement is 4 cm, and the distance passed within is 100 cm