Assertion: On a rainy day, it is difficult to drive a car or bus at high speed.
Reason: The value of coefficient of friction is lowered due to wetting of the surface.

Statement 1 : It is difficult to drive a vehicle at high speed on a rainy day. Statement 2: Friction is independent of the area of contact between the surfaces.

These questions consists of two statements each printed as Assertion and Reason. While answering these question you are required to choose any one of the following five reponses (a) If both Assertion and Reason arecorrect and Reason is the correct explanation of Asserrtion. (b) If both Assertion and Reason are correct but Reason is not the correct explanation of Assertion. (c ) If Assertion is true but Reason is false. (d) If Assertion is false but Reason is true. Assertion A block of mass m starts moving on a rough horizontal surface with a velocity v. It stops due to friction between the block and the surface after moving through a certain distance. The surface is now tilted to an angle of 30^(@) with the horizontal and the same block is made to go up on the surface with the same initial velocity v. The decrease in the mechanical energy in the second situation is smaller than that in the first situation. Reason The coefficient of friction between the block and the surface decreases with the increase in the anglle of inclination.

Asseration : A block of mass m starts moving on a rough horizontal surface with a velocity v. It stops due to friction between the block and the surface after moving through a ceratin distance. The surface is now tilted to an angle of 30^@ with the horizontal and same block is made to go up on the surface with the same initial velocity v. The decrease in the mechanical energy in the second situation is small than the first situation. Reason : The coefficient of friction between the block and the surface decreases with the increase in the angle of inclination.

If a charged particle is projected on a rough horizontal surface with speed v_(0) . Find the value of dynamic coefficient of friction, if the kinetic energy of system is constant.

In the following questions, each question contains Statement I(assertion) and StatementII(reason). Each questions has four choices a, b, c, and d out of which only one is correct. Statement I: A block of mass m starts moving on a rough horizontal surface with a velocity v. It stops due to friction between the block and the surface after moving through a certain distance. The surface is now titled to an angle of 30^@ with the horizontal and the same block is made to go up on the surface with the same initial velocity v. The decrease in mechanical energy in the second situation is smaller than that in the first situation. Statement II: The coefficient of friction between the block and the surface decreases with the increase in the angel of inclination.

A modern gran -prix racing car of masses m is travelling on a flat track in a circular arc of radius R with a speed v . If the coefficient of static friction between the tyres and the track is mu_(s) , then the magnitude of negative lift F_(L) acting downwards on the car is : ( Assume forces on the four tyres are identical and g = acceleration due to gravity )

A block of mass m height 2h and width 2b rests on a flat car which moves horizontally with constant acceleration a as shown in figure. Determine a. the value of the acceleration at which slipping of the block on the car starts, if the coefficient of friction is mu . b. the value of the acceleration at which block topples about A , assuming sufficient friction to prevet slipping and c. the shortest distance in which it can be stopped from a speed of 20 ms^(-1) with constant deceleration so that the block is not disturbed. The following data are given b=0.6 m, h=0.9 mu=0.5 and g=10ms^(-2)