CBSE
Multiple Choice QuestionsA car of mass m starts from rest and accelerates so that the instantaneous power delivered to the car has a constant magnitude Po. The instantaneous velocity of this car is proportional to
t2Po
t1/2
t-1/2
t-1/2
Two similar springs P and Q have spring constants KP and KQ, such that KP>KQ. They are stretched, first by the same amount (case a), then by the same force (case b). The work done by the springs WP and WQ are related as, in case (a) and case (b), respectively
WP =WQ ;WP> WQ
WP =WQ ;WP= WQ
WP > WQ ;WQ> WP
WP > WQ ;WQ> WP
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
A block of mass 10 kg, moving in the x-direction with a constant speed of 10 ms-1 , is subjected to a retarding force F= 0.1x J/m during its travel from x = 20 m to 30 m. Its final KE will be
475 J
450 J
275 J
275 J
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 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
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
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
Two particles of masses m1,m2 move with initial velocities u1 and u2. On collision, one of the particles gets excited to a higher level, after absorbing energy (E). If final velocities of particles be v1 and v2, then we must have
A body of mass (4m) is lying in x-y plane at rest. It suddenly explodes into three pieces. Two pieces each of mass m move perpendicular to each other with equal speed (v). The total kinetic energy generated due to explosion is,
mv2
2mv2
2mv2
