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Motion in Straight Line
Question
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Two spherical bodies of masses M and 5M and radii R and 2R are released in free space with initial separation between their centres equal to 12 R. If they attract each other due to gravitational force only, then the distance covered by the smaller body before collision is

  • 2.5 R

  • 4.5 R

  • 7.5 R 

  • 1.5 R 

Answer

C.

7.5 R 

Suppose, the smaller body cover a distance x before collision, then

Mx = 5M (9R-x) 
Or,
x= 45R- 5x
Or,
x = 45 R\6 = 7.5 R

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Some More Questions From Motion in Straight Line Chapter

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Can a body be always at rest in some frame?

Can a body be in motion in the frame associated with the body itself?

When an object in motion can be considered as particle or point object?

Can you think of physical phenomena involving the moon in which moon cannot be treated as particle?

A train is crossing the bridge. Can it be taken as a particle?

Can a train be taken a particle? Give an example in support of your answer.

 A particle is moving along curved line in space. Is the motion one dimensional?

State which of the following are examples of one, two or three dimensional motion: 

(a) A kite flying in the sky.

(b) The earth revolving around the sun. 

(c) A train moving along the equator of the earth in clockwise direction. 

(d) Accelerated motion of a particle in a straight line.

Define distance.