IIT JEE Main / Advanced Physics 2018: Physics – Kind of objective questions to expect in Gravitation

As the decisive and final test looms in the horizon ( of course , we are referring to IIT JEE Main / Advanced Physics 2018 ) , physicsmynd , in it’s endeavour to provide  support to the discerning students who are appearing for the same , starts a new series based on the scientfic analysis of the previous 30 yrs question papers of IIT JEE  Physics . Here , we will be presenting the results regarding our analysis of specific sections / topics covered in the Physics syllabus and based on that , will present the kind of problems expected to be asked . In the first part of this series, we are covering gravitation. [ N.B : The whole exercise is meant to point out sections / problems which has a fair chance of being asked , however , it doesn’t neccesarily need to be asked . Moreover , students are advised to understand the theoretical principles and the workout involved therein behind each question , rather than considering the given question per se ]

The pie chart above covers the period from 1980 to 2015 . This period was considered as fifteen segments ( taken anti -clockwise , 4% dealing with the period 1980-81 and at the other end 8 % relating to 2010 -2015) and the maximum marks that could be awarded was taken as 100 % ( for the whole physics paper – objective + subjective questions ) . Equal weightage was given to the sub-topics of Gravitation. During the periods 2004 – 2005 and 1994-1995 no questions were asked from gravitation .

1. Consider a planet whose size is the same but mass five times that of earth. What is the amount of work needed to lift a mass of 6 kg vertically upwards through a distance of 4m on the planet . [ Take the g of earth as 10 m/s² ]

2. Calculate the escape velocity on the surface of a planet whose mass is 9 x 1024g and radius 1.5 x 106m .[ G = 6.67 x 10-8dyne cm²g-2 ].

3.A satellite is revolving in a circular equatorial orbit of radius R = 2 x 105 km from east to west. Find the interval after which it will appear at the same equatorial position on earth. Given that the radius of earth = 6400km and g ( acceleration due to gravity ) = 10m/s².

4.A spherical hollow is made in a lead sphere of radius R such that its surface touches the outside surface of the lead sphere and passes through the centre. The mass of the lead sphere before hollowing was M . The force of attraction that this sphere would exert on a particle of mass m which lies at a distance d from the centre of the lead sphere on the straight line joining the centres of the sphere and the hollow is — .

5.Consider two stars of masses M and 25 M with radii a and 5a respectively and having a centre – to – centre separation of 10 a. A spaceship of mass m is launched staight from the surface of the larger star towards that of the smaller star. Find the minimum initial speed of the ship if it is to reach it’s destination.

6. A tunnel is drilled along a chord of the moon , such that it’s mid point is half the moon radius away from the centre of the moon. Is it possible that a parcel dropped at one end of this hole will exexute simple harmonic motion , and if so find its period of oscillation. Also calculate the speed at the mid point of this hole.

7. A stone takes a time t1 to move down a staight tube from the surface to the centre of a uniform spherical non-rotating asteroid. If the gravitational feild due to the asteroid were to remain constant from its surface to the centre, the particle will have taken time t2 to travel the same path . Find the ratio t1 / t2 .

( to continue …… )

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