# Speed when a system is jerked into motion

• harimakenji
In summary, the problem involves two particles connected by a light inextensible string and a fixed smooth pulley. The particles are initially held at a height of 5 m above the ground and are released from rest. The tension in the string and acceleration of each particle is to be found, as well as the distance above the ground of the highest point reached by the 5 kg mass. The speed with which the system is jerked into motion and the impulse experienced by the string during the jerk is also to be determined. The height of the highest point is 10 m, taking into account the inextensibility of the string. The impulse is the change in momentum, but the meaning of "speed with which the system is
harimakenji

## Homework Statement

Two particles of masses 8 kg and 5 kg are connected to the two ends of a light inextensible string which passes over a fixed smooth pulley. Initially each of the two particles are held at a position which is 5 m above a horizontal ground. The objects are then released from rest. Assuming that the particles never reach the pulley, and also that the particles do not rebound when they strike the ground
(i) find the tension in the string and the acceleration of each particle
(ii) find the distance above the ground of the point H, the highest point reached by the 5 kg mass
(iii) find the speed with which the system is jerked into motion and the impulse experienced by the string during the jerk

## Homework Equations

Kinematics and dynamics

## The Attempt at a Solution

(i) I am able to do this

(ii) because the particles never reach the pulley, the highest point is 10 m, which is when the 8 kg-mass reaches the ground. Correct?

(iii) I do not understand this one. What is the meaning "speed with which the system is jerked into motion"? I interpreted it as the initial speed of the system and the answer should be zero? If not, maybe the speed when the particles start to move. But how to find it? I have acceleration and the initial speed is zero (because the particles are at rest and then released), but the speed depends on the time. What is the time that I should take to put to the equation of motion?

Thank you very much

(ii) Both are initially 5m above ground. what would be height of one if other is moved to ground. keep in mind that string is inextensible.

(iii) impulse is change in momentum i.e. dP
but even i don't know what "speed with which the system is jerked into motion" means

cupid.callin said:
(ii) Both are initially 5m above ground. what would be height of one if other is moved to ground. keep in mind that string is inextensible.

10 m?
(iii) impulse is change in momentum i.e. dP
but even i don't know what "speed with which the system is jerked into motion" means

This question confused me. Can anyone please interpret waht the question means?

Thank you very much

## 1. What is the definition of "jerk" in physics?

In physics, jerk is the rate of change of acceleration. It represents the change in acceleration over a specific time interval.

## 2. How does jerk affect the speed when a system is jerked into motion?

When a system is jerked into motion, the speed of the system will increase due to the sudden change in acceleration. The higher the jerk, the faster the speed will increase.

## 3. Is jerk a constant value or does it change during motion?

Jerk can vary during motion depending on the force applied to the system. If a constant force is applied, the jerk will also be constant. However, if the force changes, the jerk will also change accordingly.

## 4. How does jerk impact the stability of a system?

High jerk values can cause instability in a system, as it represents a sudden change in acceleration. This sudden change can lead to vibrations and oscillations, making the system less stable.

## 5. Can jerk be negative?

Yes, jerk can be negative if the acceleration decreases over time. This represents a decrease in speed, or deceleration, of the system.

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