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

The length of a spring is l₁ and l₂, when stretched with a force of 4 N and 5 N respectively. Its natural length is

1. l₂ + l₁

2. 2(l₂-l₁)

3. 5l₁ - 4l₂

4. 5l₂ - 4l₁

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 the radius \(r.\) The tangential speed of lighter stone is \(n\) times that of heavier stone when they experience the same centripetal forces. The value of \(n\) is:

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)

A spring of force constant k is cut into lengths of ratio 1:2:3. They are connected in series and the new force constant is $k^{\text{'}}$. If they are connected in parallel and force constant is $k^{\text{'}\text{'}}, then k^{\text{'}}:k^{\text{'}\text{'}}$ is 

(1) 1:6

(2) 1:9

(3) 1:11

(4) 6:11

A rigid ball of mass m strikes a rigid wall at ${60}^{°}$ and gets reflected without loss of speed as shown in the figure. The value of impulse imparted by the wall on the ball will be 

(1) mv

(2) 2mv

(3) mv/2

(4) mv/3

A bullet of mass 10g moving horizontal with a velocity of 400 m/s strikes a wood block of mass 2 kg which is suspended by light inextensible string of length 5 m. As result, the centre of gravity of the block found to rise a vertical distance of 10 cm. The speed of the bullet after it emerges of horizontally from the block wiil be 

(1) 100 m/s 

(2) 80 m/s

(3) 120 m/s 

(4) 160 m/s 

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 on the 4 kg block, then the contact force between A and B is
                            

1.2N

2. 6N

3. 8N

4. 18N