# Describe the motion of the rock particle at point B during t

• physicsSOS
In summary, earthquakes produce transverse and longitudinal seismic waves that travel through rock. Figure 8 shows the displacement of particles at a given instant for different positions along a transverse wave. At point B, the particle will oscillate from equilibrium to maximum positive displacement, back to equilibrium, then to maximum negative displacement, and back to equilibrium. The wave itself is moving forward, so at a later moment, point B will also move forward. This is because the wave moves forward, but the point only moves up and down at the same place.
physicsSOS

## Homework Statement

6 Earthquakes produce transverse and longitudinal seismic waves that travel through rock. Figure 8 shows the displacement of the particles of rock at a given instant, for different positions along a transverse wave. Figure 8:

(b) Describe the motion of the rock particle at point B during the passage of the next complete cycle. (2 marks)

## The Attempt at a Solution

So I thought that point B of the next cycle is the point at equilibrium after point C. So then I figured that the particle would move down (from point B or equilibrium) to maximum negative displacement, and then up to equilibrium. And that would be the end of the cycle (which starts at point C?). The answer however is this: (oscillates from equilibrium to maximum positive displacement, back to equilibrium, then to max negative displacement) and back to equilibrium /starting position /rest position.

So, I guess one difference is that they explained the motion during the whole cycle, but why? Aren't they asking for point B?

Notice that the wave itself is moving in the forward direction. At a later moment, that entire wave will move forward (to the right). What will happen to point B then?

fishspawned said:
Notice that the wave itself is moving in the forward direction. At a later moment, that entire wave will move forward (to the right). What will happen to point B then?

Oh... so point B will also move forward..? But still, isn't point B always going to be at that point (equilibrium after max positive) on the wave?

Careful - I think I can see where your problem is.

Consider I have a jump rope. I'll mark a spot along it. In fact if you have a rope nearby you should do this!

Now lay the rope on the floor and have it stretched out. take one end and give it a quick a up and down jerk (you are making the wave!) and that wave will travel down the length of the rope. Now ask yourself - did the rope move along with the wave? Did the marked piece of of rope travel forward with the wave when the wave reached it? t you find out.

This is a very important thing to know about waves so let me know what you find out.

Hm... I'm not sure. I couldn't find a rope or jump rope. I'm finding it hard to visualise

But if I think about it, I guess it means that at some instant, the equilibrium point before A will be at point B, since the wave is moving forward..?

thankfully you don't need a rope - use youtube!

take a look. put your finger on a point along that rope. does it move forward? the wave clearly does. But what about a point on the rope? in other words, which way does the medium move?

Nice! The wave moves forward but not the point

EXACTLY
just be sure you can tell which way the point DOES move.

The point moves up and down at the same place

## 1. What is the velocity of the rock particle at point B during t?

The velocity of an object is defined as the rate of change of its position over time. Therefore, in order to determine the velocity of the rock particle at point B during t, we would need to know its position at two different time points. Without this information, we cannot accurately determine the velocity at point B during t.

## 2. How can we calculate the acceleration of the rock particle at point B during t?

Acceleration is defined as the rate of change of velocity over time. In order to calculate the acceleration of the rock particle at point B during t, we would need to know its velocity at two different time points. Without this information, we cannot accurately determine the acceleration at point B during t.

## 3. What factors can affect the motion of the rock particle at point B during t?

The motion of the rock particle at point B during t can be affected by various factors such as external forces acting on the particle, the shape and size of the particle, and the medium it is moving through. Other factors such as air resistance and friction can also impact the motion of the particle.

## 4. Can the motion of the rock particle at point B during t be accurately predicted?

In order to accurately predict the motion of the rock particle at point B during t, we would need to have a thorough understanding of all the factors that can affect its motion. Additionally, we would need precise measurements of the initial conditions and the ability to account for any uncertainties. In some cases, the motion of the particle may be unpredictable due to chaotic or random events.

## 5. How does the motion of the rock particle at point B during t relate to Newton's laws of motion?

The motion of the rock particle at point B during t can be described by Newton's laws of motion. The first law states that an object will remain at rest or in motion with constant velocity unless acted upon by an external force. The second law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. The third law states that for every action, there is an equal and opposite reaction. These laws can be used to analyze and understand the motion of the rock particle at point B during t.

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