11.

What will be the effect on the weight of a body placed on the surface of earth, if earth suddenly ' stops rotating?

• No effect

• Weight will increase

• Weight will decrease

• Weight will become zero

A child is standing with folded hands at the centre of a platform rotating about its central axis. The kinetic energy of the system is K. The child now stretches his arms so that the moment of inertia of the system doubled. The kinetic energy of the system now is

• 2 K

• $\frac{\mathrm{K}}{2}$

• $\frac{\mathrm{K}}{4}$

• 4K

A particle is moving eastwards with a velocity of 5 m/s. In 10 s, the velocity changes to 5 m/s northwards. The average acceleration in this time is

• zero

• 1/√2 m s^-2 towards north-west

• 1/√2 m s^-2 towards north-east

• 1/√2 m s^-2 towards north

A spring of spring constant 5 x 10³ N m^-1 is stretched initially by 5 cm from the unstretched position. The work required to stretch it further by another 5 cm is

• 6.25 N m

• 1250 N m

• 18.75 N m

• 25.00 N m

According to kinetic theory of gases, molecules of a gas behave like

• inelastic spheres

• perfectly elastic rigid spheres

• perfectly elastic non-rigid spheres

• inelastic non-rigid spheres

Assertion:  The relative velocity between any two bodies moving in opposite direction is equal to sum of the velocities of two bodies.

Reason:  Sometimes relative velocity between two bodies is equal to difference in velocities of the two bodies.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false

• If both assertion and reason are false.

Assertion:  A quick collision between two bodies is more violent than a slow collision, even when the initial and the final velocities are identical. 

Reason: The rate of change of momentum is greater in the first case.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  A body subject to three concurrent forces may be in equilibrium. 

Reason: For equilibrium, the sum of all the concurrent forces acting at a point should be zero.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  The relative velocity between any two bodies moving in opposite direction is equal to sum of the velocities of two bodies. 

Reason:  Sometimes relative velocity between two bodies is equal to difference in velocities of the two bodies.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Two waves represented by y = a sin( ωt - kx )  and  y = a cos( ωt- kx ) are superposed. The resultant wave will have an amplitude

• a

• $\sqrt{2} \mathrm{a}$

• 2 a

• zero