The Traffic lights at three different road crossings change after every 48 seconds, 72 seconds and 108 seconds respectively, If they change simultaneously at 7 am at what time will they change simultaneously again ?

Find the rate of change of the area of a circle per second with respect to its radius r when r = 5 cm.

A girl riding a bicycle along a straight road with a speed of 5 ms^-1 throws a stone of mass 0.5 kg which has a speed of 15 ms^-1 with respect to the ground along her direction of motion. The mass of the girl and bicyle is 50 kg. Does the speed of the bicycle change after the stone is thrown? What is the change in speed, if so?

Current changes from 12A to 7A in 2 seconds in a coil of self inductance 2H. Find the induced emf in the coil.

What is the difference between direct current and alternating current? How many times does AC used in India change direction in one second?

Two stones are thrown up simultaneously from the edge of a cliff 200 m high with initial speeds of 15 m s^-1 and 30 m s^-1 . Verify that the graph shown in Fig. 3.27 correctly represents the time variation of the relative position of the second stone with respect to the first. Neglect air resistance and assume that the stones do not rebound after hitting the ground. Take g = 10 m s^-2 . Give the equations for the linear and curved parts of the plot.

When the current changes the direction 50 times in one second then the frequency of a.c. is 50 Hz. is this statement true.