Comprehension Questions | Physics 9th Chapter 4 Turning Effect Of Forces | National Book Foundation

2. Give a short response to the following questions
Two forces of 7N and 5N are added, how will they give resultant of 12N and 2N?
Why long spanner is used to open or tight nuts of vehicle’s tyre? While tightening a small nut, extra-long wrench is not suitable. Why?
Why door knobs are fixed at the edge of door? What will happen if the door knob is at the middle of the door?
A uniform metre rod is balanced on the sharp edge of a knife. A mass is hanging on its right side. Why is it not falling on right side?
How does this toy remain balanced on finger, even disturbed slightly?
A small boy is thrown straight up by his father. At the top of his path, he comes to rest for a moment. Will he be in equilibrium at this point?
A fan is rotating uniformly, is it in equilibrium?
Can a body be in equilibrium under the action of single force or single torque?
Give an example of a body, which satisfies first condition of equilibrium but it is not in equilibrium?
Why Heavy Transport Vehicles (HTV) are made at their bottom?
A boy standing by joining both legs is more likely to fall than a boy standing with legs wide open. If slightly pushed by another boy. Why?
Q. Give an extended response to the following questions
What are parallel forces? Differentiate between like parallel forces and unlike parallel forces. Explain with the help of a figure.
How do you add forces by the head to tail rule? Write in steps and draw figures to elaborate each step. Also define resultant force.
A vector F ⃗ is making angle θ with x-axis. Resolve F ⃗ into its components.
Find magnitude and direction of a force in terms of its components.
What is moment of force or torque? On what factors it depends? Write its mathematical formula.
What is couple? How does it help to rotate steering wheel? Derive its mathematical expression.
Define center of mass. What is the effect of mass distribution in a body on its center of mass?
What is the center of gravity? Where will be the center of gravity of these regular shaped bodies; circular plate, rectangular and square plate, triangular shaped plate, cylinder, sphere (also draw figures to support your answer). Differentiate between the center of mass and the center of gravity.
How can you find the center of gravity of an irregular shaped thin sheet of plastic?
Define equilibrium. What are its types? Give examples.
What are the conditions of equilibrium? Explain.
What are the different states of equilibrium? With the help of examples, explain each state of equilibrium.
Q4. Solve the following numerical questions.
Find the magnitude and direction of the resultant of these forces acting on a block:
A. 70N along x axis B. 50N at 30o with x axis C. 40N along y axis
An aeroplane is moving with 200m/s at angle of 60° with horizontal. Sun is shining straight above the aeroplane. What is speed of shadow of the plane on ground.
70N force is acting on a body at 60° with the horizontal. Find the magnitude of its components.
The horizontal and the vertical components of a force are 3N and 4N respectively. Find their resultant force.
Two bodies are hanging by two cords of ropes as shown. Tension in upper cord is 500N and lower cord is 200N. Find the masses of bodies.
Calculate the torque acting on a spanner of length 20cm to loosen a nut by a force of 50N. If the same nut is to loosen up by the force of 100N, what should be the length of spanner?
If a nut is loosen by 90Nm torque using a spanner of the length 30cm, then how much force is applied on the spanner?
Two masses 200g and 50g are hanging at positions 60cm and 70cm respectively on a uniform metre rod as shown. Where should the third mass of 150g be positioned to balance this metre rod as shown.
A steering wheel of diameter 2 feet is rotated by two equal and opposite forces, each of magnitude 10N. What is couple arm? Calculate the moment of couple.