Q 1. The phenomenon of motion was placed on a sound scientific footing by two scientists. Write their names.
Ans. Galileo Galilei and Isaac Newton.
Q 2. The area under the velocity-time curve represents which physical quantity?
Ans. Distance and displacement.
Q 3. Under what conditions, distance, and magnitude of the displacement are equal?
Ans. Distance and displacement are equal fan object move along a straight line in one direction.
Q 4. What is the numerical ratio of average velocity to the average speed of an object when it is moving in a straight path?
Ans. In this case, both are equal, so the ratio is 1.
Q 5. What does the speedometer of an automobile measure?
Ans. The speedometer of a vehicle measures its instantaneous speed.
Q 6. Classify the following quantities on the basis of scalar quantities and vector quantities.
(a) Distance
(b) Displacement
(c) Speed
(d) Velocity
(e) Acceleration
Ans. (a) Distance: Scalar quantity
(b) Displacement: vector quantity
(c) Speed: Scalar quantity
(d) Velocity: Vector quantity
(e) Acceleration: Vector quantity
Q 7. What will you say about the motion of an object if its distance-time graph is a straight line with having a constant angle with a time axis?
Ans. The motion of the body is uniform motion (constant speed).
Q 8. Are rest and motion absolute or relative terms
Ans. They are relative terms.
Q 9. Give one example where the displacement is zero but the distance traveled is not zero.
Ans. When a body completes one rotation in a circular path its initial and final positions are the same and hence its displacement is zero.
Q 10. Suppose a ball is thrown vertically upwards from a position P above the ground. It rises to the highest point Q and returns to the same point P. What is the net displacement and distance travelled by the ball?
Ans. Displacement is zero. Distance is twice the distance between position P and Q.
Q 11. What will you say about the motion of a body if its velocity-time graph is a straight line parallel to the time axis?
Ans. The velocity of the body is constant.
Q 12. The velocity of the body is constant.
Ans. It is velocity because velocity can be positive or negative while speed cannot be negative.
Q 13. What is the acceleration of a body moving with uniform velocity along a straight line?
Ans. Acceleration of the body is zero as the velocity is constant.
Q 14. Which speed is greater: 30 m/s or 30 km/h?
Ans. 30 m/s
Q 15. What do you mean by 2 m/s2?
Ans. The velocity of the body increases by 2 m/s after every second.
Q 16. Can uniform linear motion be accelerated?
Ans. No
Q 17. Define one radian.
Ans. It is the angle which is subtended at the centre by an arc having a length equal to the radius of the circle
Q 18. What is the relation between linear velocity and angular velocity?
Ans. . Linear velocity = Angular velocity × Radius of circular path.
Q 19. Give an example when we infer the motion indirectly.
Ans. We infer the motion of air by observing the movement of dust particles or leaves and branches of trees, or simply by feeling the blowing air on our face.
Q 20. What is essential to describe the position of an object?
Ans. We need to specify a reference point called the origin.
Q 21. What is the simplest type of motion?
Ans. Motion in a straight line.
Q 22. What indicates the motion of the earth?
Ans. The phenomenon like day and night indicates the motion of the earth.
Q 23. f the displacement of a body is zero, is it necessary that the distance coyered by it is also zero?
Ans. No. When the body comes back to the same position after travelling a distance, its displacement is zero though it has travelled some distance.
Q 24. Can the displacement be greater than the distance travelled by an object?
Ans. No, it is always either equal to or less than the distance travelled by the object.
Q 25. When do the distance and displacement of a moving object have the same magnitude?
Ans. The magnitude of distance and displacement of a moving object are same when the object moves along the same straight line in the same fixed direction.
Q 26. Does the speedometer of a car measure its average speed?
Ans. No. It measures its instantaneous speed.
Q 27. A body is moving with a velocity of 10 m/s. If the motion is uniform, what will be the velocity after 10 s?
Ans. As the motion is uniform, the velocity remains 10 m/s after 10 s.
Q28. Can a body have constant speed but variable velocity?
Ans. Yes, e.g. a body in uniform circular motion has constant speed but due to the change in the direction of motion, its velocity changes at every point.
Q 29. When is the acceleration taken as negative?
Ans. Acceleration is taken as negative if it is in the direction opposite to the direction of velocity.
Q 30. What is uniform acceleration?
Ans. Acceleration of an object is said to be uniform if it travels in a straight line and its velocity increases or decreases by equal amounts in equal intervals of time.For example, motion of a freely falling body.
Q 31. Give an example of non-uniform acceleration.
Ans. A car is travelling along a straight road increases its speed by unequal amounts in equal intervals of time.
Q 32. How are the distances travelled by an object related to the time taken when an object travels equal distances in equal intervals of time?
Ans. In this case, distance travelled by the object is directly proportional to the time taken.
Q 33. What would be acceleration of a body if its velocity-time graph is a line parallel to the time axis?
Ans. Zero, as the body possesses uniform velocity.
Q 34. Is the motion of a body uniform or accelerated if it goes round the sun with constant speed in a circular orbit?
Ans. It is accelerated, as its velocity changes due to change in direction.
Q 35. Give an example of a body which may appear to be moving for one person and stationary for the other.
Ans. The passengers in a moving bus observe that the trees, buildings as well as the people on the roadside appear to be moving backwards. Similarly, a person standing on the roadside observes that the bus (along with its passengers) is moving in forward direction. But, at the same time, each passenger in a moving bus or train observes, his fellow passengers sitting and not moving. Thus, we can tell that motion is relative.
Q 36. How can we describe the location of an object?
Ans. To describe the position of an object we need to specify a reference point called the origin.
For example, suppose that a library in a city is 2 km north of the railway station. We have specified the position of the library with respect to the railway station i.e., in this case, the railway station acts as the reference point.
Q 37. What do you mean by average speed? What are its units?
Ans. Average speed is defined as the average distance travelled per unit time and is obtained by dividing the total distance travelled by the total time taken. The unit of average speed is the same as that of the speed, that is, ms-1.
Q 38. What do you understand by instantaneous velocity?
Ans. Instantaneous velocity is the velocity of a body at any particular instant during its motion. For example, the instantaneous velocity of a motorcycle at a particular instant is 40 kmh-1 if it is moving at 40 kmh-1 at that particular instant. It is measured by the speedometers on the vehicles.
Q 39. What is negative acceleration?
Ans. If the velocity of a body decreases with time, then its final velocity is less than the initial velocity and thus its acceleration is negative. Negative acceleration is called retardation or deceleration. For example, when brakes are applied to a moving truck, its velocity gradually decreases. In other words, it is under retardation.
Q 40. Differentiate between distance and displacement.
Ans.
Q 41. What are the uses of a distance-time graph?
Ans. The various uses of a distance-time graph are as follows:
- It tells us about the position of the body at any instant of time.
- From the graph, we can see the distance covered by the body during a particular interval of time.
- It also gives us information about the velocity of the body at any instant of time.
Q 42. The data regarding the motion of two different objects P and Q is given in the following table. Examine them carefully and state whether the motion of the objects is uniform or non-uniform.
Ans. We can see that the object P covers a distance of 10 m in every fifteen minutes. In other words, it covers equal distance in equal interval of time. So, the motion of object P is uniform. On the other hand, the object Q covers 7 m from 9:30 am to 9:45 am, 4 m from 9:45 am to 10:00 am, and so on. In other words, it covers unequal distance in equal interval of time. So, the motion of object Q is non-uniform.
Q 43. What are the characteristics of distance-time graph for an object moving with a non-uniform speed?
Ans. The characteristics of distance-time graph for a non-uniform speed are:
- It is always a curve (parabola).
- The speed of the moving object at any point is given by the slope of the tangent to the curve at that point.
Q 44. Given below is the velocity-time graph for the motion of the car. What does the nature of the graph show ? Also find the acceleration of the car.
Ans. The nature of the graph shows that velocity changes by equal amounts in equal intervals of time. For a uniformly accelerated motion, velocity-time graph is always a straight line.
As we know, acceleration is equal to the slope of the graph
Q 45. Four cars A, B, C and D are moving on a levelled road. Their distance versus time graphs are shown in figure. Which car is the slowest?
Ans. Speed = Slope of distance-time graph. The smaller the slope, the smaller is the speed.
From the figure, slope is minimum for car D. So, D is the slowest car.
Q 46. The table given below shows distance (in cm) travelled by bodies A, B and C. Read this data carefully and answer the following questions.
(i) Which of the bodies is moving with
(a) constant speed?
(b) constant acceleration?
(c) non-uniform acceleration?
(ii) Which of the bodies covers
(a) maximum distance in 3rd second?
(b) minimum distance in 3rd second?
Ans.
(i) (a) Body A (b) Body C (c) Body B
(ii) (a) Body C. Total distance travelled = 100 – 60 = 40 cm
(b) Body B. Total distance travelled = 24 – 36 = (-) 12 cm
The negative sign implies decceleration.
Q 47. Define the following terms:
(a) Distance
(b) Displacement
(c) Speed
(d) Velocity
(e) Acceleration
(f) Uniform motion
(g) Uniform circular motion
(h) Scalar quantity
(i) Vector quantity
Ans.
(a) Distance: The total path length traveled by a body in a given interval of time is called distance.
(b) Displacement: The shortest distance measured from the initial to the final position of an object is known as displacement.
(c) Speed: The speed of a body is defined as the distance traveled per unit time.
(d) Velocity: Velocity is defined as displacement per unit time.
(e) Acceleration: The rate of change of velocity with respect to time.
(f) Uniform motion: A body moving in a straight line has a uniform motion if it travels the equal distance in equal intervals of tune.
(g) Non-uniform motion: A body has a non-uniform motion if it travels unequal distances in equal intervals of time.
(h) Scalar quantity: A physical quantity which is described completely by its magnitude only, is called a scalar quantity.
(i) Vector quantity: A physical quantity that has magnitude as well as direction and obeys the vector addition is called a vector quantity.
Q 48. Draw position-time graph of a body that started from a position other than origin and moving with uniform speed.
Ans.
Q 49. What ¡s the nature of the distance-time graph for accelerated motion?
Ans.
Q 50. Distinguish between speed and velocity.
Ans. Speed
- Speed is the ratio of distance and time.
- Speed is always positive
- Speed is a scalar quantity.
Velocity:
- Velocity is the ratio of displacement and time.
- Velocity may be negative or positive.
- Velocity is a vector quantity.