A circular park of radius 20 m is situated in a colony. Three boys Ankur, Syed and David are sitting at equal distance on its boundary each having a toy telephone in his hands to talk each other. Find the length of the string of each phone.

Three girls skating on a circular ice ground of radius 200 m start from a point P on the edge of the ground and reach a point Q diametrically opposite to Pfollowing different paths as shown in Fig. 4.20. What is the magnitude of the displacement vector for each ? For which girl is this equal to the actual length of path skate?

The class X students of a secondary school in Krishinagar have been allotted a rectangular plot of land for their gardening activity. Saplings of Gulmohar are planted on the boundary at a distance of 1m from each other. There is a triangular grass lawn in the plot as shown in the figure. The student are to sow seeds of flowering plants on the remaining area of the plot. Taking A as origin, find the coordinates of the vertices of the triangle.

The two parallel circular loops of wire shown in fig each have a radius R = 20 cm and are separated by a distance a = 0.5 cm. The bottom loop is held fixed and the top loop hangs from one end of the arm of an equal arm balance. Since a is much smaller than R, the magnetic field produced by one loop at the other is practically the same as if both were long straight wires. if the curret in each loop is 20 A, how big is the force of attraction of one loop for the other?

A man stands on a rotating platform, with his arms stretched horizontally holding a 5 kg weight in each hand. The angular speed of the platform is 30 revolutions per minute. The man then brings his arms close to his body with the distance of each weight from the axis changing from 90cm to 20cm. The moment of inertia of the man together with the platform may be taken to be constant and equal to 7.6 kg m^2 :- What is his new angular speed? (Neglect friction.)

The two parallel circular loops of wire shown in fig each have a radius R = 20 cm and are separated by a distance a = 0.5 cm. The bottom loop is held fixed and the top loop hangs from one end of the arm of an equal arm balance. Since a is much smaller than R, the magnetic field produced by one loop at the other is practically the same as if both were long straight wires. if the current in each loop is 20 A. How much additional mass m must be added to the right-hand pan of the balance to keep the loops separated by 0.5 cm, when the currents are turned on?

A man stands on a rotating platform, with his arms stretched horizontally holding a 5 kg weight in each hand. The angular speed of the platform is 30 revolutions per minute. The man then brings his arms close to his body with the distance of each weight from the axis changing from 90cm to 20cm. The moment of inertia of the man together with the platform may be taken to be constant and equal to 7.6 kg m^2 :- Is kinetic energy conserved in the process? If not, from where does the change come about?

Two chords AB and CD of lengths 5 cm and 11 cm respectively of a circle are parallel to each other and are on opposite sides of its centre. If the distance between AB and CD is 6 cm, find the radius of the circle.