{"id":515,"date":"2019-08-09T03:43:12","date_gmt":"2019-08-08T22:13:12","guid":{"rendered":"https:\/\/www.physicsacademyonline.com\/blog\/?p=515"},"modified":"2021-02-25T14:02:15","modified_gmt":"2021-02-25T08:32:15","slug":"blog-15-created-24-07-2018-you-solve-jee-main-2017-paper-1-with-a-smile","status":"publish","type":"post","link":"https:\/\/www.physicsacademyonline.com\/blog\/jee-main\/blog-15-created-24-07-2018-you-solve-jee-main-2017-paper-1-with-a-smile.html","title":{"rendered":"SOLVE JEE (MAIN) 2017 WITH A SMILE \u2013 II"},"content":{"rendered":"

Let Us<\/del> <\/em><\/i>YOU<\/span> Solve Physics JEE (MAIN) 2017 Physics Paper<\/i><\/h3>\n

We continue with Physics questions from JEE (Main) 2017, Paper-1. All are MCQs with single correct option. Ticking the correct option fetches full 4 marks; ticking incorrect option or multiple options fetches -1 mark. So never rely on wild guesses! Hint on every question is followed by a video solution, to be consulted strictly at the end of your own solution. The video lectures referred in the discussion can be accessed @ PhysicsAcademyOnline.com.<\/a><\/p>\n

One more thing. Our freewheeling discussion on every question will obviously consume some time. But remember! While in examination hall, you should ideally take two minutes to solve a question, and then move on to the next question. Time is, indeed, a decisive factor in competitive exams.<\/p>\n

Question 05<\/u>:<\/strong>\u00a0\u00a0 The moment of inertia of a uniform cylinder of length L and radius R about its perpendicular bisector is I. What is the ratio, L\/R, such that the moment of inertia is minimum?:<\/p>\n

(1) \u221a(3\/2)\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 (2) \u221a3\/2\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 (3) 1\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 (4) 3\/\u221a2<\/p>\n

Frankly speaking, this question is quite difficult compared to the others dealt so far at JEE (Mains) level. However, not only shall we guide you at every step to solve the question, we shall give you some practical advice as well.<\/p>\n

First, the time factor. The solution is bound to take some precious time. So just like a good batsman ducks a bouncer on occasions, you might do well to skip the question as it comes and return to solve it at the end, time permitting. It’s not wise to repent later that one question’s solution took away the time for three other questions!<\/p>\n

There is no ready-made formula for moment of inertia, I, of a cylinder about its perpendicular bisector. To calculate that, first learn the calculus-based technique from the following lecture:\u00a0 Chapter Name \u2013 Mechanics; Category \u2013\u00a0 Basic; Topic Name \u2013 Rotational Mechanics; Video Name \u2013 Moment of Inertia, and Its Calculation for Various Bodies.<\/span><\/em><\/p>\n

\"\"<\/a><\/p>\n

Let us chip in with a diagram. Take an infinitesimal disc of thickness dx at distance x from the perpendicular bisector. What is its moment of inertia, dI, about the bisector? Two more lectures will be useful: Chapter Name \u2013 Mechanics; Category \u2013\u00a0 Basic; Topic Name \u2013 Rotational Mechanics; Video Names \u2013 “Two Important Theorems on Moment of Inertia” & “Applications of Parallel and Perpendicular Axes Theorems”.<\/span><\/em><\/p>\n

Integrate dI over the length of cylinder to find I. Express it in terms of a single variable, L. Under what condition is I the minimum? Recommended a typical problem on Maxima and Minima from: \u00a0 Chapter Name \u2013 Mechanics; Category \u2013 Advanced; Topic Name \u2013 Vectors; Video Name \u2013 Advanced-Level Problems on Vectors I (problem 1).<\/em><\/span><\/p>\n

Go ahead and pick your choice. Lest it leaves any doubt in your mind, confirm from the detailed video solution below.<\/p>\n

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