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?

A particle of mass 0.3 kg is subjected to a force F = –kx with k = 15 N/m. What will be its initial acceleration if it is released from a point 20 cm away from the origin

(1) 5 m/s²

(2) 10 m/s²

(3) 3 m/s²

(4) 15 m/s²

If a person with a spring balance and a body hanging from it goes up and up in an aeroplane, then the reading of the weight of the body as indicated by the spring balance will 

(1) Go on increasing

(2) Go on decreasing

(3) First increase and then decrease

(4) Remain the same

A man is standing at a spring platform. Reading of spring balance is 60 kg-wt. If a man jumps outside the platform, then reading of spring balance:

(1) first increases then decrease to zero.

(2) decreases.

(3) increases.

(4) remains same.

A body of mass 5 kg is suspended by a spring balance on a smooth inclined plane as shown in the figure. The spring balance measure:

(1) 50 N

(2) 25 N

(3) 500 N

(4) 10 N

A block of mass 4 kg is suspended through two light spring balances A and B. Then A and B will read respectively 

(1) 4 kg and zero kg

(2) Zero kg and 4 kg

(3) 4 kg and 4 kg

(4) 2 kg and 2 kg

Three weights W, 2W and 3W are connected to identical springs suspended from a rigid horizontal rod. The assembly of the rod and the weights fall freely. The positions of the weights from the rod are such that 

(1) 3W will be farthest

(2) W will be farthest

(3) All will be at the same distance

(4) 2W will be farthest

The masses of 10 kg and 20 kg respectively are connected by a massless spring as shown in figure. A force of 200 N acts on the 20 kg mass. At the instant shown, the 10 kg mass has acceleration 12 m/sec². What is the acceleration of 20 kg mass?

(1) 12 m/sec²

(2) 4 m/sec²

(3) 10 m/sec²

(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

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