Force & Laws Of Motion (Test -1) - Class 9 Science, 21-02-2018 - Class 9 MCQ

The spring force is the force exerted by a compressed or stretched spring upon any object that is attached to it. An object that compresses or stretches a spring is always acted upon by a force that restores the object to its rest or equilibrium position. So, the spring force does not always pushes a body.

If a branch of a tree is vigorously shaken, some of the leaves may get detached from tree due to inertia of rest. The leaves tend to remain in rest but branches come in motion.

At equilibrium, the acceleration is equal to zero. So, there is no net change in acceleration of the moving body.

Inflated balloon lying on the surface of a floor moves forward when pierced with a pin due to Newton’s third law of motion. The air coming out of the balloon forces the balloon in opposite direction.

Force is the rate of change of momentum. So, momentum is constant when force is zero.

Inertia is the property of a body by virtue of which the body unable to change the state of rest or state of motion and direction as inertia is the tendency to oppose the change in state or direction.

To every action, there is an equal and opposite reaction. This is the newton’s third law of motion.

The force acting on a body is equal to rate of change of momentum. Change of momentum = 10 Kg/s, time taken = 0.01 second. Force = 10/0.01 = 1000N.

Force is the rate of change of momentum. So, momentum is constant when force is zero.

Inertia of the body is proportional to the mass of the body. 5Rs coin is heavier than 5Rs note and 1Rs coins. So, inertia of 5Rs coin more than others.

The force always occurs in pairs. According to third law of motion, there is equal and opposite reaction. So two force, action and reaction acts in pair always.

Rocket moves forward according to newton’s third law of motion. The gas and other substance coming out from the tail push the rocket in forward direction. Newton’s laws are universal.

One Newton (1N) is equal to 105 dyne. Both dyne and Newton is unit of force.

A high jumper runs for a while before taking high jump so that the inertia of motion help him in taking a long jump. Inertia of motion tends to remain in state of motion.

Frictional force always opposes relative motion between the surfaces of contact. The direction of force is always in opposite direction.

When body is dropped from height, the potential energy deceases and kinetic energy increases. A ball dropped from height will conserve only kinetic energy.

A force has both magnitude as well as direction. Force is a vector quantity. Force is the product of mass and acceleration.

The inertia of the body is proportional to mass of the body. So, body P with masses 10 kg will have more inertia in comparison to body Q of mass 5 kg.

The two forces acting on same body, which are equal and opposite direction forms action and reaction. This is the newton’s thirds law of motion.

The velocity of the body falling towards depends upon gravitational force acting on it. So, both the body of masses 1 kg and 5 kg will have same velocity at particular height and fall at same time at the ground.

Gravitational force is very weak force as it depends upon mass of the body and distance between two objects. Electrostatic force is non-contact force.

Action and reaction are equal and opposite but even they do not cancel each other because they acts in opposite direction. Hence the statement is correct.

The branch of mathematics, called Calculus was stated by Newton. Force is the product of mass and acceleration. So, acceleration= force /mass. Doubling of force will increase the acceleration if mass is kept same.

The ball moving on level ground comes to rest after covering a short distance due to frictional force acting on it. So, ball slows to a stop because there is a force on the ball opposing the motion.

Newton’s third law of motion explains action and reaction. Action and reaction acts simultaneously, are equal in magnitude. They act on different direction and acts on different body.

If an object experience a net zero unbalanced force, than the body moves with constant velocity. Zero unbalanced force due to produce acceleration in the body.

Force = 7 kg-wt = 7×107×10 = 70 N, mass = 10 kg. therefore, acceleration produced in the body = F/a = 70/10 
= 7 ms-2.