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 lift is going up. The total mass of lift and the passenger is \(1500\) kg. The variation in the speed of the lift is as given in the graph. The tension in the rope pulling the lift at \(t=11^{\text{th}}\) s will be:

      
1. \(17400\) N
2. \(14700\) N
3. \(12000\) N
4. zero

A player caught a cricket ball of mass 150 gm moving at a rate of 20 m/s. If the catching process be completed in 0.1 s, then the force of the blow exerted by the ball on the hands of the player is 

1. 0.3 N

2. 30 N

3. 300 N

4. 3000 N

A rocket has a mass of 100 kg. 90% of this is fuel. It ejects fuel vapours at the rate of 1 kg/sec with a velocity of 500 m/sec relative to the rocket. It is supposed that the rocket is outside the gravitational field. The initial upthrust on the rocket when it just starts moving upwards is:

1. Zero

2. 500 N

3. 1000 N

4. 2000 N

In which of the following cases, a force will not be required to keep the:

1. particle going in a circle.

2. particle going along a straight line.

3. momentum of the particle constant.

4. acceleration of the particle constant.

A ball of mass 150g starts moving with an acceleration of 20 m/s² when hit by a force, which acts on it for 0.1 sec. The impulsive force is:

1. 0.5 N-s

2. 0.1 N-s

3. 0.3 N-s

4. 1.2 N-s

A body, whose momentum is constant, must have a constant: 

1. force.

2. velocity.

3. acceleration.

4. All of these

Rocket engines lift a rocket from the earth surface because hot gases with high velocity:

1. push against the earth.

2. push against the air.

3. react against the rocket and push it up.

4. heat up the air which lifts the rocket.

A force of 50 dynes is acted on a body of mass 5 g which is at rest for an interval of 3 seconds, then impulse is 

1. $0.15\times {10}^{-3}Ns$

2. $0.98\times {10}^{-3}Ns$

3. $1.5\times {10}^{-3}Ns$

4. $2.5\times {10}^{-3}Ns$