Work, Energy an...

A ball dropped from a height of 4m rebounds to a height of 2.4m after hitting the ground. Then the percentage of energy lost is

A body of mass m₁ is moving with a velocity v. It collides with another stationary body of mass m₁. They get embeded. At the point of collision, the velocity of the system

Assertion : In the elastic collision between two bodies, the relative speed of the bodies after collision is equal to the relative speed before the collision.
Reason : In the elastic collision the linear momentum of the system is conserved.

Assertion : When a gas is allowed to expand, work done by gas is positive.
Reason : Force due to gaseous pressure and displacement (of position) on in the same direction.

Assertion : A light body and heavy body have same momentum. Then they also have same kinetic energy.
Reason : Kinetic energy does not depend on mass of the body.

Assertion : Mountain roads rarely go straight up the slope.
Reason : slope of mountains are large, therefore, more chances of vehicle to slip from roads.

Assertion : The mass equivalent of 1000 kwh energy is 40 microgram.
Reason : This follows from E = mc² where C = 3 × 10⁸ m/s

Assertion : Two bodies of different masses have same momentum. Their kinetic energy are in the inverse ratio of their masses.
Reason : K.E. = 1/2 mv²

Assertion : Linear momentum is conserved in both, elastic and inelastic collisions.
Reason : Total energy is conserved in all such collisions.