Electric Ball!

A solid spherical ball is kept at the edge of the table. The region has uniform electric field in horizontal direction (in the direction ball tends to fall) .We give it a slight push. What is the angle (measured clockwise) , which it makes with the vertical at the time it loses its contact with table.

Your answer can be represented as -

θ = π 4 sin 1 ( a b c ) \theta = \frac{\pi}{4} - {\sin}^{-1}(\frac{a}{b\sqrt{c}}) .

Enter your answer as a × b × c a \times b \times c .

Details and Assumptions

  • The mass of ball is m = 2 kg m = 2\text{ kg} , Radius of ball is R = 0.5 m R = 0.5 \text{ m} , charge on ball is q = 4 μ C q = 4\mu C (uniformly distributed on this dielectric ball). Electric field E = 5 × 10 6 N / C E = 5 × {10}^{6} N/C , take g = 10 m/s 2 g = 10 \text{ m/s}^2 .

  • a , b a,b and c c are positive real numbers. a a and b b are coprime and c c is a square-free integer.

  • There is sufficient friction to prevent slipping .


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The answer is 340.

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2 solutions

Sibasish Mishra
Mar 10, 2017

Relevant wiki: Rotational Kinetic Energy - Conservation of Energy

bro @Aniket Sanghi could'nt you just ask the answer in simpler terms ? the trigo was difficult for me than physics !(just kidding ) first we have to conserve energy and don't forget the work done by electric forces and then at the point of loss of contact Normal reaction = 0 after you do this stuff you should get the answer , i would have uploaded a pic but my camera is not working !

Can u tell me how u solved the trigo? I also got those equations

Md Junaid - 3 years, 7 months ago

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Multiply and divide by √2 and manipulate to get the sin(a-b) form

Arunava Das - 3 years, 4 months ago

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