A body of weight 50 N placed on a horizontal surface is just moved by a force of 28.2 N. The frictional force and the normal reaction are

(1) 10 N, 15 N

(2) 20 N, 30 N

(3) 2 N, 3 N

(4) 5 N, 6 N

A rough vertical board has an acceleration ‘a’ so that a 2 kg block pressing against it does not fall. The coefficient of friction between the block and the board should be

(1) > g/a

(2) < g/a

(3) = g/a

(4) > a/g

It is easier to draw up a wooden block along an smooth inclined plane than to haul it vertically, principally because 

(1) The friction is reduced

(2) The mass becomes smaller

(3) Only a part of the weight has to be overcome

(4) ‘g’ becomes smaller

A lead ball strikes a wall and falls down, a tennis ball having the same mass and velocity strikes the wall and bounces back. Check the correct statement

(1) The momentum of the lead ball is greater than that of the tennis ball

(2) The lead ball suffers a greater change in momentum compared with the tennis ball

(3) The tennis ball suffers a greater change in momentum as compared with the lead ball

(4) Both suffer an equal change in momentum

A ball of weight 0.1 kg coming with speed 30 m/s strikes with a bat and returns in opposite direction with speed 40 m/s, then the impulse is (Taking final velocity as positive) 

(1) $-0.1\times \left(40\right)-0.1\times \left(30\right)$

(2) $0.1\times \left(40\right)-0.1\times (-30)$

(3) $0.1\times \left(40\right)+0.1\times (-30)$

(4) $0.1\times \left(40\right)-0.1\times \left(20\right)$

A ball of mass m falls vertically to the ground from a height h₁ and rebound to a height h₂. The change in momentum of the ball on striking the ground is 

(1) $mg(h_1-h_2)$

(2) $m\left(\sqrt{2g{h}_1}+\sqrt{2g{h}_2}\right)$

(3) $m\sqrt{2g(h_1+h_2)}$

(4) $m\sqrt{2g}(h_1+h_2)$

An elevator and its load have a total mass of 800 kg .Find the tension in the supporting cable when the elevator, moving downward at 10 m/s is brought to rest with constant acceleration in a distance of 25 m. ( Take g = 10m/s² ) :-

(1) 6400 N

(2) 8000 N

(3) 9600 N

(4) Zero

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

1. g, g/3

2. g/3, g

3. g, g

4. g/3, g/3

A car is negociating a curved road of radius R. The road is banked at angle $\mathrm{\theta }$. The coefficient of friction between the car and the road is ${\mu }_s$. The maximum safe velocity on this road is 

(a)$\sqrt{gR\left(\frac{\tan \theta +\mu s}{1-{\mu }_s\tan \theta }\right)}$ 

(b) $\sqrt{\frac{g}{R}\left(\frac{\tan \theta +\mu s}{1-{\mu }_s\tan \theta }\right)}$

(c) $\sqrt{\frac{g}{R^2}\left(\frac{\tan \theta +\mu s}{1-{\mu }_s\tan \theta }\right)}$

(d) $\sqrt{g{R}^2\left(\frac{\tan \theta +\mu s}{1-{\mu }_s\tan \theta }\right)}$

A 40 kg slab rests on a frictionless floor as shown in the figure. A 10 kg block rests on the top of the slab. The static coefficient of friction between the block and slab is 0.60 while the kinetic friction is 0.40. The 10 kg block is acted upon by a horizontal force 100 N. If g = 9.8 m/s², the resulting acceleration of the slab will be 

(1) 0.98 m/s²

(2) 1.47 m/s²

(3) 1.52 m/s²

(4) 6.1 m/s²