Chapter Unit - 1 : Force, Work, Energy and Power - Contact and Non-contact Forces - Frank Solutions for Class 10 Physics ICSE

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Chapter 1 - Force, Work, Energy and Power - Contact and Non-contact Forces Excercise 10

Question 1
What is meant by the term force?
Solution 1
A force is that physical force which changes or tends to change the state of rest or state of motion of the body. It can start or stop the body. It can change the speed or direction or both of body. It can bring about change in dimensions of the body.
Question 2
What are contact forces? Give two examples.
Solution 2
Contact forces are forces which come into play when the bodies come into physical contact with each other, e.g. frictional forces, force of normal reaction. These forces are produced by way of action and reaction.
Question 3
What are non-contact forces? Give two examples.
Solution 3
Non-contact forces are forces which act on the bodies through the empty space without coming into any physical contact. Also known as action at a distance force or field forces, for example: gravitational forces, electrostatic forces.
Question 4
Give one example, in each case, of a force that:
(i) Pushes         (ii) pulls
(iii) Lifts         (iv) resists
Solution 4
(i) We push a door to close it.
(ii) A railway engine pulls a train
(iii) The force that a passenger applies to put a luggage on the platform into the train is a lifting force.
(iv) When we try to move heavy roller, it resists our effort to move it.
Question 5
Give one example of a force that stretches.
Solution 5
When a normal spring held between the hands is pulled outward, we stretch it.
Question 6
Give one example of a force that compresses.
Solution 6
we push a piston fitted inside a cylinder containing gas, we compress the gas.
Question 7
How is the unit of force kgf related to Newton?
Solution 7
1 kgf = 9.8 newton
Question 8
Write the SI unit of force. Define it.
Solution 8
The SI unit of force is 'newton'.
One newton is the force which when acts on a body of mass 1kg, produces an acceleration of 1ms-2, i.e.
1 newton = 1 kg x 1ms-2
Question 9
Write the CGS unit of force. How is it related to the SI unit of force?
Solution 9
In CGS system, the unit of force is 'dyne'.
1 newton = 1kg x 1 ms-2
             = 1000 g x 100 cms-2
             = 105 dyne
Question 10
What is the relationship between kgf and N?
Solution 10
1 kgf = 9.8 newton
Question 11
Give one example of a force causing change in size of the body.
Solution 11
When a balloon is inflated the force of air inside changes it shape or size.
Question 12
State one factor on which the magnitude of a non-contact force depends.
Solution 12
The magnitude of a non-contact force depends upon the distance between the two objects.
Question 13
What are balanced forces? Give two examples.
Solution 13
When the resultant of a group of forces acting on the same object is zero, the forces are said to be balanced. Balanced forces do not change the speed of stationary objects. They may deform objects.
e.g. An iron ball suspended from a hook by a wire, a book kept on a table.
Question 14
What are non-balanced forces? Give two examples.
Solution 14
When the resultant of a group of forces acting on the same object is not equal to zero, the forces are said to be unbalanced. An unbalanced force changes the state of constant velocity including zero velocity of a body on which it acts.
e.g. If you push a ball, it starts to roll; Applying a force to stop a cricket ball.
Question 15
Classify the following amongst the contact and non-contact forces:
(i)    tension in the string,
(ii)    magnetic force,
(iii)    normal reaction force,
(iv)    gravitational force of attraction,
(v)    force of attraction between unlike charges.
Solution 15
(i) Contact force
(ii) Non-contact force
(iii) Contact force
(iv) Non-contact force
(v) Non-contact force
Question 16
What is the relationship between 1 kgf and N?
Solution 16
1 kgf = force due to gravity on 1 kg mass
        = 1 kg mass x acceleration due to gravity g in ms-2
        = g newton
1 kgf = 9.8 newton
Question 17
What is the meaning of the following statement?
1 kilogram force (kgf) = 9.8 newton
Solution 17
It means that 1 kgf  or one kilogramme force is the force due to gravity on 1 kilogram mass.
Question 18
State the effects that a force can produce. Give one example of each effect.
Solution 18
Effects a force can produce and examples:
1. Change the state of rest; e.g. pushing a door to open it or close it.
2. Change the state of motion; e.g. applying a force to stop the cricket ball.
3. Change the direction of motion and not speed; e.g. when a force is applied to move a body in a circular    path with uniform speed there is only a change in direction of motion but speed remains constant.
4. Change both speed and direction of motion; e.g. when a body is swirled in the vertical circle its direction    of motion and speed changes at every point.
5. Change the dimension; when a balloon is inflated the force of air inside changes its shape or size.

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