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.
By the system against a conservative force
The potential energy of a system increases if work is done by the system against a conservative force.
-ΔU = Wconservative face
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
B.
19.2 kW
Potential difference (drop) between two cities = 150 x 8 = 1200 V
Average resistance of total wire = 0.5 x 150 = 
Power loss, P = 
= 19.2 kW
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
B.
2/3 mgR
Change in potential energy,
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.
1.5 x 1020
Efficient power P= 
A ball is thrown vertically downwards from a height of 20m with an initial velocity vo, It collides with the ground, loses 50% of its energy in collision and rebounds to the same height. The initial velocity vo is,
(Take g = 10 ms-2)
14 ms-1
20 ms-1
28 ms-1
28 ms-1
B.
20 ms-1
Suppose a ball rebounds with speed v,
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