Force and Pressure Test - 17

$$\textbf{Hint}$$ Apply newton's second law of motion.

STEP (1):  SI Unit

 Force acting on the body may affect the shape of the body or it will accelerate or decelerate the body, or it will give motion to the static body or it will stop the motion of the dynamic body.

                                     $$F = ma$$

   Where   $$'F'$$ = force applied,  $$'m'$$ = mass  and   $$'a'$$ = acceleration 

                           Acceleration   $$a = \dfrac vt$$

    Where   $$v$$  = velocity     (in m/s)

    Here   $$'m'$$  is mass  and  $$'s'$$   is  seconds

    Time   $$'t'$$  is in seconds

Therefore  acceleration unit is = $$\dfrac{\dfrac ms}s = \dfrac m{s^2}$$

Hence unit of force  =  $$kg \dfrac m{s^2} =  Newton$$   (in S.I. unit)  i.e, option $$D$$ is a unit of force

Newton can converted into Pound  

that is  1 Newton = 0.22481  pound  ( in FPS system )  i.e, option $$A $$ is unit of force

  $$\textbf{Step2:CGS Unit}$$

   $$F = \dfrac{g.cm}{s^2} = Dyne$$  (in C.G.S. unit)  i.e, option $$ B $$ is a unit of force

Here  $$'g'$$  is grams  , $$'cm'$$  is centimeters  and  $$'s'$$ is  seconds

Conclusion:  Joule is the correct answer because it is the unit of energy.

A non-contact force is a force applied to an object by another body that is not in direct contact with it. The most familiar example of a non-contact force is weight.

Opening a door requires our hand to apply force by pushing and pulling which is a contact force. There is some frictional force in the door hinge, against that we apply force. The hinge friction is again a contact force.

To lift an object upwards it has to be pulled upwards, vertically.

An archer uses his muscular strength to pull a bow. Thus option A is correct.

The goalkeeper applies a force on the ball in the opposite direction to that of its motion and thus stops the ball.

By kicking a body, we apply a force towards the center of mass of the body, thus kicking is a pushing force whereas lifting, opening, and picking are the pulling forces. 

Effort is defined as a force exerted by a machine or in a process.

A non-contact force is a force applied to an object by another body that is not in direct contact with it. eg: gravitational force.
Gravitational force: the force of attraction that exists among all bodies that have mass.
The force exerted on each body by the other through weight is proportional to the mass of the first body times the mass of the second body divided by the square of the distance between them.

Coulomb electrostatic force of attraction acts between the two bodies which are separated by a finite distance, hence it is non contact force since the two bodies need not to be in contact with each other whereas the rest of the forces are contact forces.