Which one of the following statements is incorrect?

1. Rolling friction is smaller than sliding friction.

2. Limiting value of static friction is directly proportional to normal reaction.

3. Frictional force opposes the relative motion.

4. Coefficient of sliding friction has dimensions of length.

A massless and inextensible string connects two blocks A and B of masses 3m and m, respectively. The whole system is suspended by a massless spring, as shown in the figure. The magnitudes of acceleration of A and B immediately after the string is cut, are respectively:
      

1. $\frac{g}{3},g$

2. g, g

3. $\frac{g}{3},\frac{g}{3}$

4. $g,\frac{g}{3}$

One end of the string of length ‘l’ is connected to a particle of mass ‘m’ and the other end is connected to a small peg on a smooth horizontal table. If the particle moves in a circle with speed 'v', the net force on the particle (directed towards the centre) will be: (T represents the tension in the string)

1. $T+\frac{m{v}^2}{l}$

2. $T-\frac{m{v}^2}{l}$

3. Zero

4. T

A block of mass m is placed on a smooth inclined wedge ABC of inclination θ as shown in the figure. The wedge is given an acceleration 'a' towards the right. The relation between a and $\mathrm{\theta }$ for the block to remain stationary on the wedge is:
         

1. $a=\frac{g}{\cos ec\theta }$

2. $a=\frac{g}{\sin \theta }$

3. $a = g\cos \theta$

4. $a = g\tan \theta$

A car is negotiating a curved road of radius R. The road is banked at an angle θ. The coefficient of friction between the tyre of the car and the road is ${\mathrm{\mu }}_{\mathrm{s}}$. The maximum safe velocity on this road is

 $1. \sqrt{\mathrm{gR}\left(\frac{{\mathrm{\mu }}_{\mathrm{s}}+\mathrm{tan\theta }}{1-{\mathrm{\mu }}_{\mathrm{s}}\mathrm{tan\theta }}\right)}$

$2. \sqrt{\frac{\mathrm{g}}{\mathrm{R}}\left(\frac{{\mathrm{\mu }}_{\mathrm{s}}+\mathrm{tan\theta }}{1-{\mathrm{\mu }}_{\mathrm{s}}\mathrm{tan\theta }}\right)}$

$3. \sqrt{\frac{\mathrm{g}}{{\mathrm{R}}^2}\left(\frac{{\mathrm{\mu }}_{\mathrm{s}}+\mathrm{tan\theta }}{1-{\mathrm{\mu }}_{\mathrm{s}}\mathrm{tan\theta }}\right)}$

$4. \sqrt{{\mathrm{gR}}^2\left(\frac{{\mathrm{\mu }}_{\mathrm{s}}+\mathrm{tan\theta }}{1-{\mathrm{\mu }}_{\mathrm{s}}\mathrm{tan\theta }}\right)}$

A plank with a box on it at one end is gradually raised about the other end. As the angle of inclination with the horizontal reaches 30^o, the box starts to slip and slides 4.0 m down the plank in 4.0 s. The coefficients of static and kinetic friction between the box and the plank will be, respectively:
          

1. 0.6 and 0.6

2. 0.6 and 0.5

3. 0.5 and 0.6

4. 0.4 and 0.3

Two stones of masses m and 2m are whirled in horizontal circles, the heavier one in a radius $\frac{r}{2}$ and the lighter one in radius r. The tangential speed of lighter stone is n times that of the value of heavier stone when they experience same centripetal forces. The value of n is-

1. 2

2. 3

3. 4

4. 1

Three blocks A, B, and C of masses 4 kg, 2 kg, and 1 kg respectively, are in contact on a frictionless surface, as shown. If a force of 14 N is applied to the 4kg block, then the contact force between A and B is: 
       

1. 2 N

2. 6 N

3. 8 N

4. 18 N

A block A of mass ${\mathrm{m}}_1$ rests on a horizontal table. A light string connected to it passes over a frictionless pulley at the edge of the table and from its other end, another block B of mass m₂ is suspended. The coefficient of kinetic friction between block A and the table is ${\mathrm{\mu }}_{\mathrm{k}}$. When block A is sliding on the table, the tension in the string is:

A system consists of three masses m₁, m_2, and m₃ connected by a string passing over a pulley P. The mass m₁ hangs freely, and m₂ and m₃ are on a rough horizontal table (the coefficient of friction = μ). The pulley is frictionless and of negligible mass. The downward acceleration of mass m₁ is : (Assume m₁ = m₂ = m₃ = m) 
          

1. $\frac{g(1-g\mu )}{9}$

2. $\frac{2g\mu }{3}$

3. $\frac{g(1-2\mu )}{3}$

4. $\frac{g(1-2\mu )}{2}$