**Page 100**

**(1)** An object has moved through a distance. Can it have zero displacement? If yes, support your answer with an example?

**Ans-** Yes, displacement can be zero if the object returns at the initial point.

**Eg:-** Let an object starts from Point A and reaches to point B after covering a distance 10 m. Then it moves towards Point A and reaches there.

**(2)** A farmer moves along the boundary of a square field of side 10 m in 40 s. What will be the magnitude of displacement of the farmer at the end of 2 minutes 20 seconds from his initial position?

**Ans-**

**(3)** Which of the following is true for displacement?

**(a)** It cannot be zero.

**(b)** Its magnitude is greater than the distance travelled by the object.

**Ans- (a)** It cannot be zero.

The above statement is true. Because displacement can be zero if object returns to the initial position.

**(b)** It is not true. Because displacement is the smallest distance in between final position and initial position of the object.

**Page 102**

**(1)** Distinguish between speed and velocity.

**Ans-** Differences between speed and velocity are tabulated below-

SN |
Speed |
Velocity |

1 |
The rate of motion of an object to find out the distance travelled by the object in unit time. | The rate of motion in specific direction of an object to find out the distance travelled by the object in unit time. |

2 |
It can be calculated with the help of distance travelled by the object. | It can be calculated with the help of displacement travelled by the object. |

3 |
Non – uniform | Can be uniform and non uniform |

4 |
Eg :- The car travelles 20 m in 10 sec. | Eg:- The car travels 20 m in north from the point A in 10 sec. |

**(2)** Under what conditions is the magnitude of average velocity of an object equal to its average speed?

**Ans-** The magnitude of average velocity of an object is equal to its average speed when we not consider direction of the velocity.

**(3)** What does the odometer of an automobile measure?

**Ans-** The odometer of an automobile measures distance covered by automobile.

**(4)**What does the path of an object looks like when it is in uniform motion?

**Ans-** The path of an object looks like a straight line when it is in uniform motion.

**(5)** During an experiment, a signal from a spaceship reached the ground station in five minutes. What was the distance of the spaceship from the ground station? The signal travels at the speed of light, that is, 3 ×10^{8} ms^{-1.}

**Ans- **

**Page 103**

**(1)** When will you say a body is in **(i) **uniform acceleration? **(ii)** Non – uniform acceleration?

**Ans-**

**(i)** When an object changes its velocity by equal amount in every one second is called constant or uniform acceleration.

**(ii)** When an object changes its velocity by unequal amount in every one second is called non – uniform acceleration.

**Page 107**

**(1)** What is the nature of the distance – time graphs for uniform and non – uniform motion of an object?

**Ans-**

The distance – time graphs for uniform motion of an object will be a straight line as represented below –

The distance – time graphs for non -uniform motion of an object will not be a straight line as represented below –

**(2)** What can you say about the motion of an object whose distance – time graph is a straight line parallel to the time axis?

**Ans-** If distance – time graph of an object is a straight line parallel to the time axis it shows that the object is stationary.

**(3)** What can you say about the motion of an object if its speed – time graph is a straight line parallel to the time axis?

**Ans-** If speed – time graph of an object is a straight line parallel to the time axis it shows that the object is moving with uniform speed.

**(4)** What is the quantity which is measured by the area occupied below the velocity – time graph?

**Ans-** The area occupied below the velocity – time graph is the distance travelled by the object.

**(6)** Fig below shows the distance – time graph of three objects A, B and C. Study the graph and answer the following questions:

**(a)** Which of the three is travelling the fastest?

**(b)** Are all three ever at the same point on the road?

**(c)** How far has C travelled when B passes A?

**(d)** How far has B travelled by the time it passes C?

**Ans-**

**(8)** The speed – time graph for a car is shown is fig below-

**(a)** Find how far does the car travel in the first 4 seconds. Shade the area on the graph that represents the distance travelled by the car during the period.

**(b)** Which part of the graph represents uniform motion of the car?

**(9)** State which of the following situations are possible and give an example for each of these:

**(a)** an object with a constant acceleration but with zero velocity

**(b)** an object moving with an acceleration but with uniform speed.

**(c)** an object moving in a certain direction with an acceleration in the perpendicular direction.

**Ans-**

**(a)** Yes, an object can move with constant acceleration but zero velocity.

**Eg:-** If a ball throw upward and reaches at certain height. Its velocity will be zero but it has acceleration due to gravitational force.

**(b)** Yes, an object can move with acceleration but with uniform speed.

**Eg:-** In circular motion the object changed its velocity as direction changes continuously but magnitude of velocity remain same ,ie, speed of the object . The object accelerates continuously.

**(c)**Yes, an object can move in a certain direction with an acceleration in the perpendicular direction

** Eg:-** In circular motion, the direction of the object is always at the tangent of the circle but its acceleration towards the radius of the circle.

** (10)** An artificial satellite is moving in a circular orbit of radius 42250 km. Calculate its speed if it takes 24 hours to revolve around the earth.

**Helping Topics**