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Relative Nature of Motion

Now we know that motion is a relative term.So absolute motion has no meaning, right?
So aren’t Galileo’s view that earth moves around sun and the church’s old belief that sun moves around earth actually not equally correct or equally wrong?
this is a question from hc verma’s concept of physics part 1.(from short answer questions)

Deepali Gupta asked

Answer: The state of motion as well as the nature of motion is relative. When we speak about any of these without SAYING  any reference, we actually have some reference in mind.

When we say that earth is moving around the sun, it is true wrt sun. But, the actual nature of motion is unpredictable since the sun, the galaxy and all are in a state of motion. So, we can say about the nature of motion only with respect to some reference which is assumed to be at rest.

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Motion in a vertical circle and conservation of energy

A stone  tied to a string of length l is whirled around a vertical circle with the other end of the string at the centre. At a certain instant of time the stone is at the lowest position and has a speed u. What is the magnitude of change in its velocity as it reaches a position where the string is horizontal?

Answer:

Let’s assume that the potential energy at the lowest position be zero. So, when the string is horizontal, the stone has risen by a vertical height l, the length of the string which is also the radius of the vertical circle.

If v is the magnitude of velocity at the horizontal position, then according to the law of conservation of energy,

KE+PE at the lowest position = KE+PE at the horizontal position

\frac{1}{2}mu^{2}=\frac{1}{2}mv^{2}+mgl

From the equation above, v-u can be calculated.

v=\sqrt{u^{2}-2gl}

 

The following links will help you for deeper understanding and you can browse through some solved problems from the topic too.

Motion of connected system – A Numerical problem

A mass 5kg descending vertically,draws up a mass of3kg by means of a light string passing over a pulley.At the end of 4 seconds,the string breaks.How much higher 3 kg mass would go?

Post your solutions as comments to this post

Answer will be posted soon once we get responses from visitors

Homework from Projectile Motion

A projectile is projected at an angle theta with horizontal with speed u . If air resistance is taken in account , the angle with vertical at the time of hitting the ground will be a)more than (90 + theta) b)less than (90 – theta) c)(90 + theta) d)equal to theta Answer: (b) Se the figure below […]

Numerical Problem from Motion of Connected systems

Two blocks A and B of mass m1 and m2 respectively are kept in contact on a frictionless table.The experimenter pushes the block A from behind so that the blocks accelerate. If  the block A exerts a force F on the block B,what is the force exerted by the experimenter on A.

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Solving problems on Laws of Motion

Sir,in solving problems of laws of motion ,is it mandatory to take that direction as +ve in which acceleration acts?(i.e should i subtract other forces acting on a body from the forces that is acting towards the acceleration)

 

(Pranay Talukdar asks)

Answer: In general, we take the forces in the direction of acceleration (I.E, ENHANCING THE ACCELERATION) and the forces against the acceleration as negative.

The first step in solving such problems is to draw a free body diagram and represent all active forces and reactions to constraints in vector form with proper direction ad label. This will highly simplify the problem.

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An online quiz for Class 9 Physics – Force and Motion

Attempt this quiz from force and motion. This is primarily aimed at CBSE Class9 students.

A Multiple Choice Quiz from Force
The page will open in a new window. Your score will be shown on top of page in percentage. You can attempt multiple times and can improve performance.
Please post your comments if you like this feature. If you like it, we will post more such quizzes.

Wish you an excellent performance in the forthcoming examinations.

Good Luck !

A Match the Following Exercise from Force

Match the following from Force

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