2.2. Explain translatory motion and give examples of various types of translatory motion
Answer:The motion of a body along a line without any rotation is called translatory motion. The line may be straight or curved.
The motion of riders in the Ferris wheel, the motion of an object along a curved path, etc.
2.3: Differentiate between the following:
(i) Rest and motion.
(ii) Circular motion and rotatory motion.
(iii) Distance and displacement
(iv) Speed and velocity.
(v) Linear and random motion.
(vi) Scalars and vectors
(i) Difference between rest and motion.
Rest:
A body is said to be at rest if it does not change its position with respect to its surroundings.
(ii) Difference between Circular motion and rotatory motion.
The motion of an object in a circular path is known as circular motion.
The motion of the earth around the sun, A stone tied at the end of a string moving in a circle, A toy train moving on a circular track, etc.
The spinning motion of a body about its axis is called its rotatory motion.
The motion of the wheel about its axis, the motion of the ceiling fan, etc.
(iii) Difference between Distance and displacement
The length of a path between two points is called the distance between those points.
It has magnitude but no direction.
It is a scalar quantity.
It is denoted by "S".
Its SI unit is a meter (m).
It formula is S = v t
The shortest distance between two points is called displacement.
It has magnitude and direction.
It is a vector quantity.
It is denoted by "d".
Its SI unit is a meter (m).
It formula is d = v t
(iv) Difference between speed and velocity.
The distance covered by an object in unit time is called its speed.
It has magnitude but no direction.
It is a scalar quantity.
It is denoted by "v".
Its SI unit is a meter per second (ms⁻¹).
It formula is v = `\frac {S}{t}`
The rate of displacement of a body is called its velocity.
or
The distance covered by an object in unit time in a specific direction is called its speed.
It has both magnitude and direction.
It is a vector quantity.
It is denoted by `\vec v`.
Its SI unit is a meter (m).
It formula is `\vec v` = `\frac {d}{t}`
(v) Difference between Linear and random motion.
Straight line motion of a body is known as its linear motion
Aeroplanes flying straight in the air, objects falling vertically down, etc.
The disordered or irregular motion of an object is called random motion.
The motion of gas molecules, the Motion of insects, and birds, the motion of dust or smoke particles in the air, etc.
(vi) Difference between Scalars and vectors
Physical quantities which are described completely by their magnitude only are called Scalar quantities.
mass, length, time, speed, volume, work, energy, etc.
Physical quantities which are described completely by their magnitude and direction as well is called vector quantities.
velocity, displacement, force, momentum, torque, etc.
1.4. Define the terms speed, velocity, and acceleration
The distance covered by an object in unit time is called its speed.
It has magnitude but no direction.
It is a scalar quantity.
It is denoted by "v".
Its SI unit is a meter per second (ms⁻¹).
It formula is v = `\frac {S}{t}`
The rate of displacement of a body is called its velocity.
or
The distance covered by an object in unit time in a specific direction is called its speed.
It has magnitude and direction.
It is a vector quantity.
It is denoted by `\vec v`.
Its SI unit is a meter per second (ms⁻¹).
It formula is `\vec v` = `\frac {d}{t}`
Acceleration:
Acceleration is defined as the rate of change of velocity of a body.
It has magnitude and direction.
It is a vector quantity.
It is denoted by `\vec a`.
Its SI unit is a meter per second per second (ms⁻²).
It formula is `\vec a` = `\frac {vec v}{t}`
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2.5. Can a body moving at a constant speed have acceleration?
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2.6. How do riders in a Ferris wheel possess translatory motion but not rotatory motion?
1.7. Sketch a distance-time graph for a body starting from rest. How will you determine the speed of a body from this graph?
The distance-time graph for a body starting its motion from rest can be of two types 1. at a constant speed and 2. at a variable speed as shown in the following figure.
We can determine the speed of the object from both of the graphs by determining the slope of the line of the graph.
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2.8. What would be the shape of a speed-time graph of a body moving with variable speed?
When an object does not cover an equal distance in an equal interval of time then the speed of an object is called variable speed. The distance-time graph for variable speed is not a straight line but a curve line as shown below.
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2.9. Which of the following can be obtained from the speed-time graph of a body?
(i) Initial speed. (ii) Final speed. (iii) Distance covered in time t. (iv) Acceleration of motion.
Answer:From speed - time graph of a body, we can calculate all the above-given quantities i.e. (i) Initial speed. (ii) Final speed. (iii) Distance covered in time t. (iv) Acceleration of motion.
2.10. How can vector quantities be represented graphically?
Graphically, a vector can be represented by a line segment with an arrowhead. The length of the line shows the magnitude of the vector and arrowhead its direction. In the following figure, the line AB with an arrowhead at B represents a vector F. The length of the line AB gives the magnitude of the vector F on a selected scale. While the arrowhead on the line at B shows that the vector is directed from A to B.
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