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Motion in Straight Line

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Physics Part I

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Physics

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12
A car moving along a straight highway with speed of 126 km h–1 is brought to a stop within a distance of 200 m. What is the retardation of the car (assumed uniform), and how long does it take for the car to stop.

Initial space velocity space of space the space car comma space straight u equals 126 space km divided by hr space equals space 35 space straight m divided by straight s

Final space velocity space of space car comma space straight v space equals space 0 space

Before space coming space to space rest comma space

Distance space covered space by space the space car comma space straight s space equals space 200 space straight m space

Let comma space retardation space produced space in space the space car space equals space straight a

Now comma space using space the space third space equation space of space motion comma space

space space space space straight v squared space minus space straight u squared space equals space 2 as space

rightwards double arrow space left parenthesis 0 right parenthesis squared space minus space left parenthesis 35 right parenthesis squared space equals space 2 space cross times space straight a space cross times space 200

rightwards double arrow space straight a space equals space minus 35 cross times 35 over 2 cross times 200 space equals space minus 3.06 space straight m divided by straight s squared space

Time space taken space by space the space car space to space stop space is space given space by space the space first space equation space of space motion. space

That space is comma space

space space space space space space space straight v space equals space straight u space plus space at

rightwards double arrow space space space straight t space equals space fraction numerator left parenthesis straight v minus straight u right parenthesis over denominator straight a end fraction space equals space fraction numerator left parenthesis negative 35 right parenthesis over denominator left parenthesis negative 3.06 right parenthesis end fraction space equals space 11.44 space sec
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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. 
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What is the most essential thing to study the motion of a body?

The most essential thing to study the motion is reference frame. Rest and motion are relative terms. It means that an object in one situation can be in rest but in another situation, the same object will be in motion. 
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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. 
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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. 
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Can a body be always at rest in some frame?

Yes, a body is always at rest in a frame which is fixed with the body itself. 
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