September 26, 2015

Junior Inter Physics Imp Questions - Laws of Motion Chapter

Q: Explain advantages and disadvantages of friction. (8 marks)
A: Safe walking on the floor, motion of vehicles are possible due to friction.
Nails, Screws are driven into walls due to friction. Mechanical Power
transmission of belt drive is possible due to friction.

Due to friction wear and tear of mechanics increases.
Heat generated due to friction, decreases the efficiency of engine.
Friction results in the large amount of power loss in engines.

Q: Mention the methods used to decrease friction.

A: Polishing: By polishing the surfaces of contact, friction can be reduced.
Bearings: The hard steel balls called bearings placed between the
moving parts converts sliding friction into rolling friction hence
friction is reduced.

Lubricants: Lubricants like oil or grease which spreads over the
surface and fills the irregularities of the surface, there by friction
is reduced.
Streamlining: Automobiles and aeroplanes are streamlined to reduce the
friction due to air.

2 Marks Questions:

Q: What is inertia? What gives the measure of inertia?
A: The inability of a body to change its state of rest or state of
motion by itself is known as inertia. Mass is measure of inertia.

Q: If a bomb at rest explodes into two pieces, the pieces must travel
in opposite directions. Explain.
A: According to Law of Conservation of linear momentum MU = m1v1 +
m2v2 Initially bomb is at rest U = 0
∴ m1v1 = − m2v2
−ve sign indicates that pieces must travel in opposite direction.

Q: Can the coefficient of friction be greater than one?
A: Yes, when the contact surfaces are heavily polished, then the
adhesive forces between molecules increases and coefficient of
friction will be greater than one.

Q: Why does the car with a flattened tyres stop sooner than the one
with inflattened tyres?
A: Flattened tyre deforms more than inflattened tyre. Due to greater
deformation of tyre rolling friction is large, hence it stops sooner.

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