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: Total energy is negative for a bound
system.
Reason: Potential energy of a bound system is
negative and more than kinetic energy.

• 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.

A 4 kg roller is attached to a massless spring of spring constant k = 100 N/m. It rolls without slipping along a frictionless horizontal road. The roller is displaced from its equilibrium position by 10 cm and then released. Its maximum speed will be

• 0.5 m s^-1

• 0.6 m s^-1

• 0.4 m s^-1

• 0.8 m s^-1

Assertion:  In elastic collision, kinetic energy is conserved. 

Reason:  Energy is always conserved.

• 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 assertion is true but reason is false.

78.

Assertion: KE is conserved at every instant of (elastic) collision.
Reason: No deformation of matter occurs in elastic collision.

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

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

• If assertion is true but reason are false.

• If both assertion and reason are false.

Whenever a stream of electrons collides with a stream of photons, in this collision, which of the following is not conserved?

• Linear momentum

• Total energy

• No. of photons

• No. of electrons

A block of mass  10 kg  is moving in x-direction with a constant speed of 10 m/s. It is subjected to a retarding force F = 0·1 x joule /metre during its travel from  x= 20 m  to  x = 30 m. Its final KE will be

• 475 J

• 450 J

• 275 J

• 250 J