Matric Notes Physics 9th Ch 4 Turning Effect of Forces Short Questions
Q1) Can the rectangular components of the vector be greater than the vector itself? Explain.
Answer: No, the rectangular components cannot be greater than the resultant vector.
The resultant of a vector i.e. force vector ‘F’ is given by the equation;
F = √(Fx2 + Fy2)
or F2 = Fx2 + Fy2
where F is the resultant vector
and Fx and Fy are the components of that vector.
It is clear from the equation that the sum of the square of rectangular components is equal to the square of the magnitude of the vector. Therefore, the rectangular components of a vector cannot be greater than the vector itself.
Q2) Explain why door handles are not put near hinges?
Answer: The door rotates about the hinges due to torque. Mathematically, torque is defined as
Torque = perpendicular distance from the axis of rotation × force applied
It can be seen from above formula that, torque depends upon the
1) Applied force.
2) The moment arm of the force.
If the door handle is put near the hinges then the distance from the hinges to the handle decreases (moment arm of force become very small) hence a large amount of force is required to produce a torque to open/close the door, therefore.
If the door handle is put far from hinges, little force is required to produce a large amount of torque and it open/close the door easily.
Q3) Can a small force ever exert a greater torque than a larger force? Explain.
Answer: Yes, a small force may exert a greater torque than a large force. Mathematically, torque is defined as
Torque = perpendicular distance from the axis of rotation × force applied
It can be seen from above formula that, torque depends upon the
1) Applied force.
2) The moment arm of the force.
So, if the moment arm is greater then less force will be required to produce a large torque. Similarly, if the moment arm is very small then a very large amount of force is required to produce the same torque.
Q4) Why it is better to use a long spanner rather than a short one to tighten a nut on a bolt?
Answer: We know the equation of torque
Torque = perpendicular distance from the axis of rotation × force applied
It can be seen from above formula that, torque depends upon the
1) Applied force.
2) The moment arm of the force.
It is clear that it is better to use a long spanner rather a short one to tight a nut. In the long spanner, the moment arm for the rotation of the nut increases, which decreases the required force to tighten the nut. Therefore, it is better to use a long spanner than a short one to open or tighten a nut.
Q5) The gravitational force acting on a satellite is always directed towards the centre of the earth: Does this force exert a torque on satellite?
Answer: According to the definition of torque;
Torque = perpendicular distance from the axis of rotation × force applied
The gravitational force acting on a satellite is always directed towards the center of the earth, so this is a central force (centripetal force). For the central force, torque is zero because the applied force is passing through axis of rotation, has zero moment arm zero.
Q6) Can we have situations in which an object is not in equilibrium, even though the net force on it is zero? Give two examples.
Answer: Yes, we can have situations in which an object is not in equilibrium, even though the net force is not zero.
1) Turning a spanner requires two hands to move, so an opposite torque acts on it making a couple. The net force, in this case, is zero, but the net torques are not zero so it is not in equilibrium.
2) Turning a steering also produce couple so the net force is zero but the net torques are not.
Q7) Why do tightrope walkers carry a long, narrow rod?
Answer: A tightrope walker uses a long rod to balance its centre of mass. If the centre of mass shift to one side, gravity will exert a torque on the acrobat, tending to cause a rotation about the rope and consequently fall.
To stay balanced, the acrobat must create a counter-torque having equal magnitude and opposite sign. That is why tightrope walkers carry a long pole.
Q8) Why does wearing high-heeled shoes sometimes cause lower back pain?
Answer: Wearing heels causes lower back to lean forward more than normal because when a person wears high heels, the center of gravity shifts from the previous position to a new forward position. As a result of which the person loses the balance. In order to maintain the balance that person has to exert force on his lower back which causes lower back pain.
Q9) Why is it more difficult to lean backwards. Explain?
Answer: The balance of our body is maintained by our brain. When someone leans forward, the visual senses see the whereabouts of the forward side and the person’s brain work out to shift the centre of gravity to keep the person balanced. But when someone leans backwards the visual senses cannot see the whereabouts of the backward side hence it becomes difficult for the brain to shift the centre of gravity to keep the person balanced.
Q10) Can a single force applied to a body change both it’s translational and rotational? Explain.
Answer: Yes, a single force may produce both rotational and translation motion in the body.
When the line of action of single force passes through the center of gravity of the body, it produces acceleration.
Whereas when the line of action of a single force is not passing through the center of gravity, it produces rotation.
Q11) Two forces produce the same torque. Does it follow that they have the same magnitude? Explain.
Answer: No, because torque depends on both force and moment arm. So for same torque, we can have different forces with different moment arms.
For Example: Suppose a 5 N force is applied to a nut by a spanner of length 2 m, the torque produced on the nut will be 10 Nm.
Similarly, for a spanner of length 4 m, a force of 2.5 N is required to produce a torque of 10 Nm.
Q12 Why is at more difficult to lean back word?
Ans. It is more difficult to lean back word because in such cases the center of gravity of the body is disturbed due which the stability decreases and it becomes more difficult to remain in state of equilibrium.
Q13 Why does a helicopter has a second rotor on its tail?
Ans. According to 2nd condition of equilibrium if the sum of all forces acting on a body is equal to zero then the body will be in state of equilibrium. That’s why there is a 2nd rotor on the tail of helicopter, the torque produced by 1st rotor is cancelled by the torque produced by 2nd rotor and this helicopter remains in state of equilibrium.
Q14 Why is it better to use a long spanner rather than a short one to tighten a nut on a bullet?
Ans. As we know that torque depends upon the moment arm “r” an “f” as long spanner has greater moment of arm. There for it is better to use long spanner rather than a short spanner to tighten a nut on a Bolt easily.
Q15 A girl is seated safety and steady canoe but when she tries to stand up the canes capsize explain this in term of c. m and stabile?
Ans. As the girl stand up the center of gravity and the e.m of body gets higher than its original position as result the stability decreases and this canoe capsizes.
Post a Comment