Advertisement

What is rest?


When an object does not change its position with time, with respect to it's surroundings. In such a case the object is said to be at rest. 
1215 Views

Advertisement
Is absolute rest or absolute motion possible?

Absolute rest and absolute motion is not possible because there is no point in the universe which is at rest and can be taken as point of reference. The planet Earth is in continuous motion. 
1986 Views

Figure 3.25 gives a speed-time graph of a particle in motion along a constant direction. Three equal intervals of time are shown. In which interval is the average acceleration greatest in magnitude ? In which interval is the average speed greatest ? Choosing the positive direction as the constant direction of motion, give the signs of v and a in the three intervals. What are the accelerations at the points A, B, C and D?


Acceleration is given by the slope of the speed-time graph.

Since the slope of the given speed-time graph is maximum in interval 2, the average acceleration will be the greatest in this interval.

The height of the curve from the time-axis gives the average speed of the particle.
In the given graph, it is clear that the height is the greatest in interval 3.
Hence, the average speed of the particle is the greatest in interval 3.

In interval 1:

The slope of the speed-time graph is positive. Hence, acceleration is positive. Similarly, the speed of the particle is positive in this interval.

In interval 2:

The slope of the speed-time graph is negative. Hence, acceleration is negative in this interval. However, speed is positive because it is a scalar quantity.

In interval 3:

The slope of the speed-time graph is zero. Hence, acceleration is zero in this interval. However, here the particle acquires some uniform speed. It is positive in this interval.

Points A, B, C, and D are all parallel to the time-axis. Hence, the slope is zero at these points. Therefore, at points A, B, C, and D, acceleration of the particle is zero. 
187 Views

What is motion?

When an object changes it's position with time, with respect to it's surroundings, the object is said to be in motion. 
657 Views

A shell of mass m is at rest initially. It explodes into three fragments having masses in the ratio 2 : 2 : 1. The fragments having equal masses fly off along mutually perpendicular direction with speed v. What will be the speed of the third (lighter) fragment ?


We can represent in the form of a figure as

Now if we use the conservation of momentum we get

o = (2m) v cos 45° + (2m) v cos 45° + mv1

So, v1 = − 4 cos 45° v = − 22 , thus the velocity of the third part has a magnitude equal to 22 v, this makes an angle of 135° with respect to either of the three masses.


Advertisement