**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.