Two cities are 150 km apart. electric power is sent from one city to another city through copper wires. The fall of potential per km is 8 V and the average resistance per km is 8 V and the average resistance per km is . The power loss in the wire is,

• 19.2 W

• 19.2 kW

• 19.2 J

• 12.2 kW

The potential energy of a system increase if work is done

• By the system against a conservative force

• By the system against a nonconservative

• upon the system by a conservative force

• upon the system by a conservative force

A 200 W sodium street lamp emits yellow light of wavelength 0.6 um. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is

• 1.5 x 10²⁰

• 6 x 10¹⁸

• 62 x 10²⁰

• 62 x 10²⁰

A ball is thrown vertically downwards from a height of 20m with an initial velocity v_o, It collides with the ground, loses 50% of its energy in collision and rebounds to the same height. The initial velocity v_o is,
(Take g = 10 ms^-2)

• 14 ms^-1

• 20 ms^-1

• 28 ms^-1

• 28 ms^-1

A body of mass m taken from the earth's surface to the height equal to twice the radius (R) of the earth. The change in potential energy of the body will be

• mg2R

• 2/3 mgR

• 3 mgR

• 3 mgR