Forces - class-IX

One object exerts a force on the other object due to their mutual interaction when the objects either are in contact with each other or placed at certain distance apart.

To move a car, their must be interactions between the men and the car. The interaction is exerted in terms of push and the car moves in the direction of push, i.e., in the direction of the force applied.

The action involved to open the door of refrigerator is pulling the force is applied to pull the door of the refrigerator. 

Force is a push or pull which changes or tends to change the state of rest or of uniform motion.

A force can change or tend to change shape, size of a body or its state of rest or direction of motion.

Contact forces are those types of forces which result when the two interacting objects are perceived to be physically contacting each other. Examples of contact forces include frictional forces, tensional forces, normal forces, air resistance forces, and applied forces.

Two bodies must interact in order to apply a force.

All Options are correct, as in each sports, Badminton racket, Javelin, bowling ball is pushed.

Resultant force, 

$ \vec F _{net} = \vec F _1 +\vec F _2$

Given,

The net force is either sum or difference of individual applied forces. So, the force is either larger or smaller than individual forces.

Unequal and opposite forces do not cancel out each other completely and thus resulting in net force acting in a particular direction. A set of such forces is called a set of unbalanced forces.

Balanced forces cancel out the effect of each other. Thus, no net external force acts on the body and hence a body at rest does not move.

If the forces on the object are balanced, this means that the individual force cancel out each other resulting in a zero net force acting on the object.

Force could be larger or smaller than the other.the strength of a force is usually expressed by its magnitude.

Unbalanced forces result in a non-zero net external force acting on a body which produces an acceleration of the body in a particular direction and hence the body at rest starts to move in that direction. Thus unbalanced forces are necessary to cause a non moving object to start moving. Thus option D is correct.

When your friend joins you, both of you push the roller in same direction. So, your forces, being applied in same direction, add up to a larger value. Thus the roller moves faster.

If applied force acts on a body in the direction of motion,the speed of the body will increase.

If the direction of force on the body is opposite to the direction of motion,the speed will decrease.

The net force on the rope is 100 N - 70 N = 30 N. The mass is 5 kg, so acceleration a = F_net / m = 30 / 5 = 6 m/s^2 upwards. For the bottom half (mass 2.5 kg), the forces are Tension T and gravity (2.5 * 10 = 25 N). T - 25 = m_half * a = 2.5 * 6 = 15. Thus, T = 40 N. Wait, re-evaluating: The force at the midpoint is the average of the forces at the ends if the rope is uniform and acceleration is constant. (100 + 70) / 2 = 85 N.

If two forces act on an object in the same direction, the net force is equal to the sum of the two forces. This always results in a stronger force than either of the individual forces alone.

Hence, the net force is the sum of forces

Using conservation of momentum: m1 * v1 + m2 * v2 = (m1 + m2) * v_final. Here, 2.5 * 2 + 0.2 * 0 = (2.5 + 0.2) * v_final. 5 = 2.7 * v_final. v_final = 5 / 2.7 = 1.8518 m/s.

The force of the gravitational pull is 500 N and the additional force of 220 N is applied in the opposite direction.
So, to lift the box, the box has to apply an extra force of 500 N - 220 N = 280 N in order to lift the box against the gravitational pull.
Resultant force is nothing but the total force acting on a body including their directions. Here, the gravitational force acts opposite to the force applied by the father and the boy.
Hence, the boy has to apply a force of 280 N to lift the box.

$1N={10}^{5}dyne$

We know that, $kg m{s}^{-1}$ is the unit of momentum. Rest all are units of $Force$.

A force could be larger or smaller than the other and the strength of the force is expressed by its magnitude only. For example, $1\ N$ of force is larger than $1\ mN$ of force.

The forces acting on the object in the opposite directions are equal. The net force will be the difference of the two equal forces. Since both the forces are equal, net force is zero.

Force, $F = mg$    where $m = 1$ gram  and $g = 981$ $cm/s^2$

If a set of forces acting on a body does not change the state of rest or of motion of an object such forces are called balanced forces. In this case object is said to be in equilibrium state. The vector sum of all forces is zero i.e. $\sum Fx = 0$.
Set of forces acting on body results in change in state i.e. either changes the speed or direction, such forces are called unbalanced forces.  In this case the object is in non-equilibrium state and the resultant force is non-zero. i.e. $\sum Fx \neq 0$.

Balanced forces always result in a zero external force acting on an object  i.e  $F _{ext}  =0$

Force applied by team A:        $F _A = 200\ N$           (towards A)

Unbalanced forces produce a resultant force acting on the object in a particular direction which tends the object to accelerate in that particular direction.

When forces are applied inn the opposite directions, the forces get subtracted.
So, net force on the body$=(5-2)N=3N$

Two engines set one after another will increase the pull.

Force applied by you $= 30 N =$ force applied by any of your friends.
So, let there be $x$ people in total to push the roller.
When $x$ people, each giving a force of $30N$, give force in same direction, total force = $30xN$
To move the roller, $30x=300$
So, $x=\frac{300}{30}=10$
$\therefore$ number of friends to join you $=(10-1)=9$

When forces are applied from opposite directions, the forces get subtracted. So, the resultant or net force is less than the force which you were applying initially. As a result, the ball will move at a slower speed.

In general, more than one force may be acting on an object.However,the effect on the object is due to the net force acting on it will be null.

If two forces act in the opposite directions on an object,the net force acting on it is the difference between the two forces.

If the force acts at an angle to the direction of motion,it can change the speed as well as the direction of motion.

A force may not always succeed in bringing a change in the state of motion of an object.

When equal and opposite force is applied it do not let the body to move,but cause change in shape of the body.

When a small body hits a very large body,then the forces acting on both the bodies are equal in magnitude but opposite in direction.However the effect (of force)produced in the small body is very large as compared to the effect of (the equal)force on the larger body.

Forces applied on an object in the same direction add to one another.

If two forces axt in the opposite directions on an object,the net force acting on it is the difference between the two forces

Here all the three force will not keep the particle in equilibrium$,$

Answer is C.

The S.I. unit of force is Newton, the absolute unit of force in the International System of Units (SI units). It is defined as that force necessary to provide a mass of one kilogram with an acceleration of one metre per second per second.

Force = $\displaystyle 5: : \frac{kg\times m}{sec^{2}}$
If unit of length and time are doubled and the unit of mass is halved
Then the unit of force will be $\displaystyle \left ( \frac{\frac{1}{2}\times 2}{(2)^{2}} \right )=\frac{1}{4}$ times
Hence the numerical value of the force will be 4 times (as numerical value $\displaystyle \propto\frac{1}{unit}$)

Dyne is unit of force specified in CGS system. 

Resultant force is nothing but the total force acting on a body including their directions. If the object is at rest or it moves with a same velocity, the resultant force should be zero. All forces are acting on same direction, resultant force should be the sum of all the forces.

In this case, the forces applied by team A are 100 N, 120 N and 170 N. The total force is 100 N+120 N+170 N = 390 N. The forces applied by tema B are 130 N, 150 N and 155 N. The total force is 130 N+150 N+155 N=435 N.
Now, both the total forces are in the opposite direction as the team are in the opposite direction. So, the resultant force is 435 - 390 = 45 N. 
Therefore, Team B will win in the game as they apply more force of 45 N.

If the body is accelerating, then there is a net force which drives the body. Since the body is accelerating, velocity can not be zero or moving with a constant speed. 
It is not necessary that the two forces must act in the same line however they may act in the same line.

Given that $F=at+bt^2$ where $t$ is time.

When two forces are applied on a object in the same direction, forces added up and net force increases.

When two forces are applied in opposite directions, the net force becomes the difference of the two. So, the net force becomes small and the table becomes difficult to move.

In SI system of units, force is expressed in Newtons ($N$).

In a game of tug-of-war, teams apply forces in terms of pulls on the rope. On the rope, two pulls act in opposite directions. The net force becomes the difference of the two forces (pulls) and the rope moves in the direction of the larger force (pull).

When you and your friend pushes heavy table in the same direction, the force applied by you and your friend get added. So, applied forces sum up to get a larger force. Hence the table moves easily.

When two forces are applied in the opposition direction on an object, the net force will be the difference between the two forces.