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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 ball is dropped from  a high-rise platform at t=0 starting from rest. After 6s another ball is thrown downwards from the same platform with a speed v. The two balls meet at t= 18s. What is the value of v? (take g= 10 ms-2)

  • 74 ms-2

  • 55 ms-1

  • 40 ms-1

  • 60 ms-1


A.

74 ms-2

For space first space ball space comma space straight u space equals space 0
therefore comma
straight s subscript 1 space equals space 1 half space gt subscript 1 superscript 2 space equals space 1 half space straight x space straight g space left parenthesis 18 right parenthesis squared
For space second space ball comma space initial space velocity space equals space straight v
therefore comma space
straight s subscript 2 space equals space vt subscript 2 space plus space 1 half space gt squared
straight t subscript 2 space equals space 18 minus 6 space equals space 12 space straight s
straight s subscript 2 space equals space straight v space straight x space 12 space plus space 1 half straight g space left parenthesis 12 right parenthesis squared
Here comma space space straight s subscript 1 space equals space straight s subscript 2
1 half straight g left parenthesis 18 right parenthesis squared space equals space 12 space straight v space plus space 1 half space left parenthesis straight g right parenthesis space left parenthesis 12 right parenthesis squared
straight v equals space 74 space ms to the power of negative 1 end exponent
For space first space ball space comma space straight u space equals space 0
therefore comma
straight s subscript 1 space equals space 1 half space gt subscript 1 superscript 2 space equals space 1 half space straight x space straight g space left parenthesis 18 right parenthesis squared
For space second space ball comma space initial space velocity space equals space straight v
therefore comma space
straight s subscript 2 space equals space vt subscript 2 space plus space 1 half space gt squared
straight t subscript 2 space equals space 18 minus 6 space equals space 12 space straight s
straight s subscript 2 space equals space straight v space straight x space 12 space plus space 1 half straight g space left parenthesis 12 right parenthesis squared
Here comma space space straight s subscript 1 space equals space straight s subscript 2
1 half straight g left parenthesis 18 right parenthesis squared space equals space 12 space straight v space plus space 1 half space left parenthesis straight g right parenthesis space left parenthesis 12 right parenthesis squared
straight v equals space 74 space ms to the power of negative 1 end exponent
1022 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 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

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

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

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