Motion
Very Short Answer Type Questions
Que:1 Mention the condition when the magnitude of the average velocity of an object is equal to its average speed.
Ans: If the body moves along a straight line.
Que:2 The phenomenon of motion was placed on a sound scientific footing by two scientists. Write their name.
Ans: Galileo Galilei and Isaac Newton
Que: 3Mention the Physical quantity shown by the slope of a velocity-time graph.
Ans: Acceleration
Que:4 Write the formula to calculate the speed of a body moving along a circular path of radius ‘r’ when it has completed n revolution in time t.
Ans: v=n x (2πr)/t
Que:5 If the time interval between lightning and thunder is 2 seconds, what is the distance of the point of lightning? (Speed of sound in air is 346 m/sec).
Ans: Since the speed of sound is lesser than the speed of light, we can neglect the speed of light.
So the distance of the lightening point, d=v x t
= 346 x2
= 692 m
Que:6 What can you say about the motion of an object whose distance-time graph is a straight line parallel to the time axis?
Ans: This means that the body is at rest and stationary.
Que:7 Give an example of a motion in which acceleration is non-uniform.
Ans: A car travelling in a straight line road increases its speed by unequal amounts in equal intervals of time.
Que:8 An object travels a distance of 16 m in 4 s and then another 16 m in 2 s. What is the average speed of the object?
Ans: Average speed= (16+16)/(4+2)=32/6=5.33 m/s
Que:9 What does the odometer of an automobile measure?
Ans: An odometer, or odograph, is a device that measures the distance travelled by an automobile based on the perimeter of the wheel as the wheel rotates.
Que:10 Does the speedometer of a car measures its average speed?
Ans: No, It measures its instantaneous speed.
Que:11 What is motion?
Ans: A body is said to be in motion if it changes its position with respect to a reference point.
Que:12 What is the simplest type of motion?
Ans: Motion in a straight line.
Que:13 Are rest and motion absolute or relative terms?
Ans: They are relative terms.
Que:14 Can an object be at rest as well as in motion at the same time?
Ans: Yes, an object may be at rest related to one object and at the same time it may be in motion related to another object.
Que:15 What indicates the motion of the earth?
Ans: The phenomena of day and night indicate the motion of the earth.
Que:16 Is speed a scalar or a vector quantity?
Ans: It is a scalar quantity.
Que:17 Give two examples of vector quantities.
Ans: Velocity and Acceleration
Que:18 What do you mean by displacement?
Ans: The shortest distance moved by a body in the direction from the initial to the final position is called displacement.
Que:19 Is displacement a scalar quantity?
Ans: No, it is a vector quantity as it has both magnitude and direction.
Que:20 If the displacement of a body is zero, is it necessary that the distance covered 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.
Que:21 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.
Que:22 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 is the same when the object moves along the same straight line in the same fixed direction.
Que:23 What is the duration of time interval needed for uniform or non-uniform motion?
Ans: It may be of any duration-small or large.
Que:24 Give two examples of non-uniform motion.
Ans: A car in a crowded street and a person jogging in a park.
Que:25 Give the technical term used for the rate of motion of a body.
Ans: Speed
Que:26 What is the S.I. unit of speed?
Ans: Meter per second i.e., m/s.
Que:27 Is it true that to specify the speed of any object we require only its magnitude?
Ans: Yes
Que:28 Covert the speed of 6 m/sec into km/hr.
Ans: 6 m/s=6 x 3600/1000=21.6 km/hr
Que:29 Name the term given to speed in a particular direction.
Ans: Velocity
Que:30 The motion of a bee flying randomly in the air is an example of this type of motion.
Ans: Non-Uniform Motion
Que: Sohan travels at 20m/s from home to tuition and returns at 25 m/s. Find his average velocity.
Ans: Since displacement is zero, the average velocity is zero.
Que: What can you say about the motion of an object whose distance-time graph is a straight line parallel to the time axis?
Ans: This means that the body is at rest and stationary.
Que: Observe the signboards on the road indicating the speed limit. What does this indication mean? Why is speeding a hazard?
Ans: The speed limit is the distance a vehicle running on the road can safely cover in 1 hour. Overspeeding threatens life and can lead to severe accidents and injuries.
Que: What is motion in a straight line?
Ans: Motion in a straight line means the body moves along x- a coordinate, a straight line. It is also called the one-dimensional motion or rectilinear motion of a particle.
Que: Give an example where the object is at rest and also in motion at the same time.
Ans: A passenger travelling in a bus is at rest with respect to his fellow passenger but is in motion with respect to the surrounding.
