{"id":198,"date":"2018-12-06T16:38:43","date_gmt":"2018-12-06T11:08:43","guid":{"rendered":"http:\/\/www.physicsacademyonline.com\/blog\/?p=198"},"modified":"2021-02-25T14:03:53","modified_gmt":"2021-02-25T08:33:53","slug":"tips-to-solve-physics-jee-advanced-2018-questions-i","status":"publish","type":"post","link":"https:\/\/www.physicsacademyonline.com\/blog\/jee-advanced-preparation\/tips-to-solve-physics-jee-advanced-2018-questions-i.html","title":{"rendered":"Tips to Solve Physics JEE (Advanced) 2018 Questions – I"},"content":{"rendered":"

Let Us<\/del> <\/em><\/i>YOU<\/span> Solve Physics JEE (Advanced 2018) Questions:<\/i><\/h3>\n

I have the JEE (Advanced) 2018, Paper-1 in front of me. This examination, which was formerly called IIT-JEE, was held on 20 May 2018. The paper contains 54 questions in total, with maximum marks 180, divided equally among Physics, Chemistry and Mathematics. Part I is Physics, having three sections: Section 1 containing six multiple-choice questions (MCQ, total marks 4 x 6 = 24), Section 2 containing eight numerical problems (total marks 3 x 8 = 24), and Section 3 containing four MCQs in two paragraphs (total marks 3 x 4 = 12). Thus, Physics Paper-1 has 18 questions carrying 60 marks in total. Considering the time allotted for the whole paper is three hours, the student ideally should solve Physics part in one hour, that is one minute allotted for one mark scored.<\/p>\n

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Let us start with Section 1, which contains six MCQs with one or more than one options correct. Obviously, this type of MCQs are more difficult than the other type having only one correct option. This reflects in the marking system: full marks only for choosing all the correct options; less marks for choosing part of the correct options; negative marking for choosing any incorrect option(s). In other words, random guesswork which is a common temptation in questions of this type is heavily penalised. So be warned!<\/p>\n

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Question 1<\/u>:\u00a0 The potential energy of a particle of mass m at a distance r from a fixed point O is given by V(r) = kr\u00b2 \/ 2, where k is a positive constant of appropriate dimensions. This particle is moving in a circular orbit of radius R about the point O. If v is the speed of the particle and L is the magnitude of its angular momentum about O, which of the following statements is\/are true?<\/p>\n

(A) v = \u221a(k\/2m). R<\/p>\n

(B) v = \u221a(k\/m). R<\/p>\n

(C) L = \u221a(mk). R\u00b2<\/p>\n

(D) L = \u221a(mk\/2). R\u00b2<\/p>\n

An alert student must have noted by now there can be only one or two correct options for this MCQ, not more. Both options (A) and (B) give a possible expression for particle speed, v, and therefore, only one of them can be correct (if not both incorrect). Similarly, both (C) and (D) give a possible expression for particle’s angular momentum, L, and hence, at most one of them can be correct. A bit of relief!<\/p>\n

Finding v first. What is the acceleration of a particle moving in a circle with constant speed? Subscribe to www.physicsacademyonline.com<\/a>, and watch the lecture following this path: Chapter Name \u2013 Mechanics; Category \u2013\u00a0 Basic; Topic Name \u2013 Circular Motion; Video Name \u2013 Derivation of Centripetal Acceleration.<\/span><\/i><\/p>\n

What force can produce such acceleration? Watch the lecture as follows: Chapter Name \u2013 Mechanics; Category \u2013\u00a0 Basic; Topic Name \u2013 Newton’s Laws of Motion; Video Name \u2013 Newton’s Second Law of Motion.<\/span><\/i><\/p>\n

Potential energy of the particle being given as a function of distance, can you deduce an alternative expression for the (conservative) force? Follow the lecture: Chapter Name \u2013 Mechanics; Category \u2013\u00a0 Basic; Topic Name \u2013 Work and Energy; Video Name \u2013 Conservative Force from Potential Energy Function, and Energy Diagrams.<\/span><\/i><\/p>\n

You are close to the answer. What is it?<\/p>\n

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Finding L next. How do you express angular momentum of a particle about any arbitrary origin as a vector product? What is its magnitude? How do you modify it for the simple case of a particle moving in a circle about the centre? Follow the discussion here: Chapter Name \u2013 Mechanics; Category \u2013\u00a0 Basic; Topic Name \u2013 Rotational Mechanics; Video Name \u2013 Angular Momentum of a Particle, and Its Relation with Torque.<\/span><\/i><\/p>\n

Only when you have completed<\/em>, confirm your answer from our MP4 video solution below.<\/p>\n