12.a) Why gravitational force are neglected when computing the force between the charged objects? b) Two charges -1 uc & +2 uc are placed at the corners A & B of an equilateral triangle ABC of side 2 m. Calculate the electric field intensity at point C. (=9x10 Nmc-2). 13.a) What is electrostatic induction? b) How a body can be charged positively by method of induction? Explain. c) State & explain coulomb's law in electrostatics. 14.Figure below shows the velocity-time graph for a vertically bouncing ball. The ball is released at A and strikes the ground at B. The ball leaves the ground at D and reaches its maximum height at E. The effects of air resistance can be neglected. a. State: B i) Why the velocity at D is negative. C ii) Why the gradient of the line AB is the same as the gradient of line DE. iii) What is represented by the area between the line AB and the time axis. iv) Why the area of triangle of ABC is greater than the area of triangle CDE. 4 Y 15. As shown in figure, a body is projected with velocity u from the point A. At the same time another body is projected vertically upwards with the velocity u from the point B. What should be the value of u, U and u/u for both the bodies to collide? Velocity 60 D 5 U 9 U E Time > X