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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 boy standing on a stationary lift (open from above) throws a ball upwards with the maximum initial speed he can, equal to 49 m s-1. How much time does the ball take to return to his hands? If the lift starts moving up with a uniform speed of 5 m s-1 and the boy again throws the ball up with the maximum speed he can, how long does the ball take to return to his hands ?

Given comma space

Initial space velocity space of space the space ball comma space straight u space equals space 49 space straight m divided by straight s
Acceleration comma space straight a space equals space – space straight g space equals space – space 9.8 space straight m divided by straight s squared space

Case space 1 colon space

The space boy space throws space the space ball space when space the space lift space is space stationary. space
Considering space that space the space motion space of space the space ball space is space upwards comma space
final space velcoity space is space zero space at space the space highest space point. space

Now comma space using space first space equation space of space motion comma space

Time space of space ascent space is space given space by comma space

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

rightwards double arrow space straight t space equals space fraction numerator left parenthesis straight v minus straight u right parenthesis over denominator straight a end fraction space

space space space space space space space equals space fraction numerator negative 49 over denominator negative 9.8 end fraction space equals space 5 space sec

Time space of space ascent space equals space time space of space descent. space

Therefore comma space

Total space time space taken space for space the space ball space to space return space
to space the space boy apostrophe straight s space hands space equals space 5 space plus space 5 space equals space 10 space sec. 

Case 2: 

Speed space with space which space the space lift space is space moving space up space equals space 5 space straight m divided by straight s

So comma space

Relatiove space velocity space of space the space ball space is space the space same
space as space it apostrophe straight s space initial space velocity.

straight i. straight e. comma space straight v space equals space 49 space straight m divided by straight s

Implies comma space the space ball space will space return space back space to space the space boy ’ straight s space
hand space after space 10 space straight s.
336 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

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. 
746 Views

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. 
650 Views

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

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