# KPK 9th Class Physics Chapter 4 Turning Effect of Forces Short Questions Answers

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Class/Subject: 9th Class Physics

Chapter Name: Turning Effect of Forces

Board: All KPK  Boards

• Malakand Board 9th Class Physics Chapter 4 Turning Effect of Forces  short questions Answer
• Mardan Board 9th Class Physics Chapter 4 Turning Effect of Forces short questions Answer
• Peshawar Board 9th Class Physics Chapter 4 Turning Effect of Forces short questions Answer
• Swat Board 9th Class Physics Chapter 4 Turning Effect of Forces short questions Answer
• Dera Ismail Khan Board 9th Class Physics Chapter 4 Turning Effect of Forces short questions Answer
• Kohat Board 9th Class Physics Chapter 4 Turning Effect of Forces short questions Answer
• Abbottabad  Board 9th Class Physics Chapter 4 Turning Effect of Forces short questions Answer
• Bannu Board 9th Class Physics Chapter 4 Turning Effect of Forces short questions Answer

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## KPK 9th Class Physics Chapter 4 Turning Effect of Forces Short Questions Answers

Can the rectangular components of the vector be greater than the vector itself? Explain

No, the rectangular components of the vector cannot be greater than the magnitude of the vector.
In fig, Fx and Fy are the rectangular components of F
Fy=Fsin0
Fx= Fcos0 and the values of sin0 and cos0 may be equal to one or less than one but cannot be greater than one so “Fx” and “Fy” may be equal to F or less than “F” but cannot be greater than “F”.

Explain why door handles are not put near hinges?

If door handles are put near the hinges. Then moment arm will be smaller so torque produced will also be smaller. Thus to produce greater torque door handles are not put near hinges because grater the moment arm, greater will be the torque produced.
τ=r×F
Thus for easy rotation of the door, the handles are put away from the hinges and not near the hinges.

Can a small force over exert a greater torque than a larger force? Explain.

Yes a small force exert a greater torque Torque depends upon two factors magnitude of force and perpendicular distance from the axis of rotation by applying a small force then a greater torque will be produced.
Example:
Case#1: F1    5N1      r1=2m
The value of torque is given by:
Then  τ1= r1 x F1
2×5
τ=10 Nm
Case#2.    F2  2N  and r2=10m
In 2nd case the value of torque is given by:
τ2 = r2F2
τ2  = 10×2
τ2=20N m
From this example it is clear that
F2< F1 but r2> r1 and  τ2>  τ1
Thus for a smaller force we can gel greater torque by taking large value of moment arm.

Why it is better to use a long spanner rather than a short one to loosen a rusty nut on a bolt?

Turning effect of a force depends upon two factors.

1. Moment arm of the force
2. Magnitude

Long spanner has large moment arm “r”. so it can produce the turning effect easily. Thus it is batter to use a long spanner rather than a short one to loosen a rusty nut.

The gravitational force acting on a satellite is always directed towards the centre of the earth. Does this force exert torque on satellite?

No, the gravitational force acting on the satellite is directed towards the centre of earth, so this is a central force. For the central force the moment arm is zero and hence torque is zero.
Hence the gravitational force on satellite does not exert torque on satellite.

Can we have situation in which an object is not in equilibrium, even though the net force on it is zero? Give two examples?

Yes the sum of forces acting on it is equal to zero and body will not be in equilibrium.
F=0
τ  =0
In such situation then the body will rotate and will not be in state of complete equilibrium.
Two force of same magnitude are acting in opposite direction with different line of action then net force acting on it is zero but body will not be in equilibrium.
Example:

1. Motion of steering wheel.
2. Motion of pedals of a bicycle

Why do tight rope walkers carry a long, narrow rod?

A tight rope walker use long narrow rod for getting balanced condition and prevent from falling. When the walker learns towards right and produce clockwise torque, then walker move the rod in such a way to produce anticlockwise torque. Clockwise and anticlockwise torque cancel the effect of each other and thus the walker will remain in state of equilibrium.

Why does wearing high heeled shoe sometime cause lower back pain?

High heeled shoe push the body in the forward direction due to which the momentum of the body in increase and force also increases. Center of gravity of the body is pushed in the forward direction.
Now to maintain the balanced condition, the body tries to oppose the forward push.
Due to this reason back muscles because tense and feel back lower pain.

Why is it more difficult to lean backwards? Explain?

It is more difficult to lean backward because in this way centre of gravity of the body is disturbed. Due to which the un-stability increases.
If we lean backward it is not possible to exert a backward force on the feel and hence we will lose our balance and will fall.

Can a single force applied to a body change both its translational and potential motion? Explain.

Yes a single force applied to a body changes both its translational and rotational motion. When a force is applied to body in such a way that its action point is other than center of mass then the body has both translational and rotational motion.
On the other hand the force is applied at the center of mass of body then the body will have only translational motion.

Two force produce the same torque. Does it follow that they have the same magnitude? Explain.

No, it is not necessary that only two force produce the same torque. Torque is defined as the product of force and moment arm of force (distance).
→  →    →
τ  = r  x F
When two different force are acting at different places from the axis of rotation we will get the same torque.
Example: when two kids of different mass are sitting at the either side of a see saw. The see saw is pivoted at its center. Adjust the position of kids from the wedge such that the sea saw is balanced in the horizontal state. We can say that:
Clockwise torque = anticlockwise torque

describe the path of the brick after you suddenly let go of the rope.
If the brick is tied to the end of the rope and whirled in a circle. The centripetal force is supplied by our hand through the rope to the brick the brick exerts a centrifugal force on our hand through the rope.
When the rope is suddenly let go the brick moves away along the tangent to the circle.

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