Assertion: Frictional forces are conservative forces. 

Reason:  Potential energy can be associated with frictional forces.

• 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 driver in a vehicle moving with a constant speed on a straight road is in a noninertial frame of reference.

Reason: A reference frame in which Newton's laws of motion are applicable is non-inertial.

• 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

Three different objects  m₁ , m₂ and  m₃ to fall from rest and from the same point O along three different frictionless paths. The speeds of the three objects, on reaching the ground, will be in the ratio of

• m₁ : m₂ : m₃

• 1 : 1 : 1

• m₁ : 2 m₂ : 3m₃

• $\frac{1}{{\mathrm{m}}_1} : \frac{1}{{\mathrm{m}}_2} : \frac{1}{{\mathrm{m}}_3}$

Assertion:  It is difficult to move a cycle along the road with its brakes on. 

Reason: Sliding friction is greater than rolling friction.

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

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

• If the assertion is true but the reason is false.

• If both assertion and reason are false.

Assertion:  In an elastic collision of two billiard balls, the total kinetic energy is conserved during the short time of oscillation of the balls (i.e. when they are in contact). 

Reason: Energy spent against friction does not follow the law of conservation of energy.

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

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

• If the assertion is true but the reason is false.

• If both assertion and reason are false.

A particle is revolving in a circle of radius R. If the force acting on it is inversely proportional to R, then the time period is proportional to

• R

• R²

• 1/R

• 1/R²

If mass of an atom M moving with speed v, what will be its speed after the emission of an α-particle is zero?

Assertion: Work done in uniform circular motion is zero.

Reason:  Force is always directed along displacement.

• 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 false but reason is true.

A ball is moving in a circular path of radius 5 m. If tangential acceleration at any instant is 10 m/s and the net acceleration makes an angle 30° with the centripetal acceleration, then the instantaneous speed is

• $50\sqrt{3}m/s$

• $9.3m/s$

• $6.6\mathrm{m}/\mathrm{s}$

• $5.4\mathrm{m}/\mathrm{s}$

A road is 8 m wide. Its radius of curvature is 40 m. The outer edge is above the lower edge by a distance of 1.2 m. This road is most suited for a velocity of

• 5.7 m/s

• 7.7 m/s

• 36.1 m/s

• 9.7 m/s