As shown in the figure, two masses of 10 kg and 20 kg, respectively are connected by a massless spring. A force of 200 N acts on the 20 kg mass. At the instant shown, the 10 kg mass has an acceleration of 12 m/s² towards the right. The acceleration of 20 kg mass at this instant is:
        
1. 12 m/s² 

2. 4 m/s² 

3. 10 m/s² 

4. Zero

What is the acceleration of block A, if the acceleration of B is 4 $\mathrm{m}/{\mathrm{s}}^2$ towards the right at the instant shown?

                          
1. \(2.5~m/s^2\)
2. \(4~m/s^2\)
3. \(5~m/s^2\)
4. Zero

Three blocks A, B and C of mass 3M, 2M and M respectively are suspended vertically with the help of springs PQ and TU and a string RS as shown in fig. The acceleration of blocks A, B and C are $a_1,a_2 and a_3$ respectively.
     

The value of acceleration \(a_{1}\) at the moment string RS is cut will be: 

1. g downward

2. g upward

3. more than g downward

4. zero

Calculate the reading of the spring balance shown in the figure: (take \(g=10\) m/s²)
                

1. \(60\) N
2. \(40\) N
3. \(50\) N
4. \(80\) N

 The length of a spring is  \(l_1\) and \(l_2\) when stretched with a force of 4 N and 5 N respectively. Its natural length is?