A car of mass m starts from rest and accelerates so that the instantaneous power delivered to the car has a constant magnitude P_o. The instantaneous velocity of this car is proportional to

• t²P_o

• t^1/2

• t^-1/2

• t^-1/2

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

93.

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 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 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

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 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

The heart of a man pumps 5 L of blood through  the arteries per minute at a pressure of 150 mm of mercury . If the density of mercury be 13.6 x 10³ kg/ m³ and g = 10 m/s², then the power of heart in watt is  

• 1.70

• 2.35

• 3.0

• 3.0

On a frictionless surface, a block of mass M moving at speed v collides elastically with another block of same mass M which is initially at rest. After collision, the first block moves at an angle θ to its initial direction and has a speed v/3/ The second block's speed after the collision is 

• 

• 3/4 v

• 

• 

An engine pumps water through a hosepipe. Water passes through the pipe and leaves it with a velocity of 2 ms^-1. The mass per unit length of water in the pipe is 100 kgm^-1. What is the power of the engine?

• 400 W

• 200 W

• 100 W

• 100 W