## Assignment for Class 9 Science Chapter 8 Motion

Class 9 Science students should refer to the following printable assignment in Pdf for Chapter 8 Motion in standard 9. This test paper with questions and answers for Grade 9 Science will be very useful for exams and help you to score good marks

### Chapter 8 Motion Class 9 Science Assignment

**Question : An object has moved through a distance. Can it have zero**

**displacement? If yes, support your answer with an example.**

**Answer :**Yes,an object can have zero displacement even when it has moved through a distance.This happens when final position of the object coincides with its initial position. For example,if a person moves around park and stands on place from where he started then here displacement

**Question : 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?**

**Answer :**

**Question : 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.**

**Answer :**None of the statement is true for displacement First statement is false because displacement can be zero. Second statement is also false because displacement is less than or equal to the distance travelled by the object.

**Question : Distinguish between speed and velocity.**

**Answer :**

**Question : Under what condition(s) is the magnitude of average velocity of an object equal to its average speed?**

**Answer :**The magnitude of average velocity of an object is equal to its average speed, only when an object is moving in a straight line.

**Question : What does the odometer of an automobile measure?**

**Answer :**The odometer of an automobile measures the distance covered by an automobile.

**Question : What does the path of an object look like when it is in uniform motion?**

**Answer :**An object having uniform motion has a straight line path.

**Question : 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}m s^{−1}.**Answer :**Speed= 3 × 10

^{8}m s

^{−1}

^{8}m s

^{−1}x 300 secs. = 9 x 10

^{10}m

**Question : When will you say a body is in (i) uniform acceleration? (ii) nonuniform acceleration?**

**Answer :**

**Question : A bus decreases its speed from 80 km h**

^{−1}to 60 km h^{−1}in 5 s. Find the acceleration of the bus.**Answer :**

**Question : A train starting from a railway station and moving with uniform acceleration attains a speed 40 km h**

^{−1}in 10 minutes. Find its acceleration.**Answer :**

**Question : What is the nature of the distance - 'time graphs for uniform and nonuniform motion of an object?**

**Answer :**When the motion is uniform,the distance time graph is a straight line with a slope.

**Question : What can you say about the motion of an object whose distance - time graph is a straight line parallel to the time axis?**

**Answer :**If distance time graph is a straight line parallel to the time axis, the body is at rest

**Question : What can you say about the motion of an object if its speed - 'time graph is a straight line parallel to the time axis?**

**Answer :**If speed time graph is a straight line parallel to the time axis, the object is moving uniformly.

**Question : What is the quantity which is measured by the area occupied below the velocity -time graph?**

**Answer :**The area below velocity-time graph gives the distance covered by the object.

**Question : A bus starting from rest moves with a uniform acceleration of 0.1 m s**

^{−2}for 2 minutes. Find (a) the speed acquired, (b) the distance travelled.**Answer :**Initial speed of the bus, u= 0

^{2}

^{–1}

^{2}- u

^{2}= 2as

^{2}- (0)

^{2}= 2(0.1) s

**Question :**

**A train is travelling at a speed of 90 km h**

^{−1}. Brakes are applied so as to produce a uniform acceleration of −0.5 m s^{−2}. Find how far the train will go before it is brought to rest.**Answer :**

^{-2}

^{2}= u

^{2}+ 2 as

^{2}= (25)

^{2}+ 2 ( - 0.5) s

^{2 }/2 ( 0.5) = 625

**Question : A trolley, while going down an inclined plane, has an acceleration of 2 cm s**

^{−2}. What will be its velocity 3 s after the start?**Answer :**Initial Velocity of trolley, u= 0 cms

^{-1}

^{-2}

^{-1}

^{-1}

**Question : A racing car has a uniform acceleration of 4 m s - '2. What distance will it cover in 10 s after start?**

**Answer :**Initial Velocity of the car, u=0 ms

^{-1}

^{-2}

^{2}

**Question : A stone is thrown in a vertically upward direction with a velocity of 5 m s**

^{−1}. If the acceleration of the stone during its motion is 10 m s^{−2}in the downward direction, what will be the height attained by the stone and how much time will it take to reach there?**Answer :**Given Initial velocity of stone, u=5 m s

^{-1}

^{-2}

^{2}- u

^{2}

### Excercise

**Question : An athlete completes one round of a circular track of diameter 200 m in 40 s. What will be the distance covered and the displacement at the end of 2 minutes 20 s?**

**Answer :**Diameter of circular track (D) = 200 m

^{1}/

_{2}

^{1}/

_{2}rounds as shown in figure

**Displacement of the athlete**with respect to initial position at x = xy

**Question : Joseph jogs from one end A to the other end B of a straight 300 m road in 2 minutes 30 seconds and then turns around and jogs 100 m back to point C in another 1 minute. What are Joseph's average speeds and velocities in jogging (a) from A to B and (b) from A to C?**

**Answer :**Total Distance covered from AB = 300 m

^{-1}

^{-1}

^{-1}

^{-1}

^{-1}

^{-1}

^{-1}

^{-1}

**Question : Abdul, while driving to school, computes the average speed for his trip to be 20 km h−1. On his return trip along the same route, there is less traffic and the average speed is 40 km h−1. What is the average speed for Abdul’s trip?**

**Answer :**The distance Abdul commutes while driving from Home to School = S

_{1}

_{2}

_{1av}= 20 km h

^{-1}

_{2av}= 30 km h

^{-1}

_{1}=S / v

_{1av}

_{2}=S/v

_{2av}

_{av}) for covering total distance (2S) = Total Dostance/Total Time

^{-1}

**Question : A motorboat starting from rest on a lake accelerates in a straight line at a constant rate of 3.0 m s**

^{−2}for 8.0 s. How far does the boat travel during this time?**Answer :**Given Initial velocity of motorboat, u = 0

^{-2}

^{2}

**Question : A driver of a car travelling at 52 km h**

^{−1}applies the brakes and accelerates uniformly in the opposite direction. The car stops in 5 s.**Another driver going at 3 km h**

^{−1}in another car applies his brakes slowly and stops in 10 s. On the same graph paper, plot the speed versus time graphs for the two cars. Which of the two cars travelled farther after the brakes were applied?**Answer :**As given in the figure below PR and SQ are the Speed-time graph for given two cars with initial speeds 52 kmh

^{-1}and 3 kmh

^{-1}respectively.

**Question : Fig 8.11 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?**

**Answer :**

**Question : A ball is gently dropped from a height of 20 m. If its velocity increases uniformly at the rate of 10 m s**

^{−2}, with what velocity will it strike the ground? After what time will it strike the ground?**Answer :**Let us assume, the final velocity with which ball will strike the ground be 'v' and time it takes to strike the ground be 't'

^{-2}

^{2}-u

^{2}

^{2}= 2as+ u

^{2}

^{-1}

**Question : The speed-time graph for a car is shown is Fig. 8.12**

**(a) Find out how far the car travels 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?**

**Answer :**

**(a)**

**(b)**

**Question : 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 in a certain direction with an acceleration in the perpendicular direction.**

**Answer :**(a) Possible

^{2}.

**Question : 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.**

**Answer :**Radius of the circular orbit, r= 42250 km

^{-1}

^{ -1}

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