Describing Motion
Class 8th Science Part I Karnataka Board Solution
- Uniform circular motion is called continuously accelerated motion because,A. direction of…
- A cricketer hits a sixer. The cricket ball moves up with a velocity of 2 ms-1 and falls…
- S I Unit of acceleration is _____________ . Fill in the blanks with suitable words…
- Velocity has both speed and _____________ . Fill in the blanks with suitable words…
- If an object starts from ‘A’ and comes back to ‘A’, its displacement will be __________ .…
- An object is moving in a circular path of radius 3.5m. If it completes one full cycle,…
- An object changes its velocity from 30 ms-1 to 40 ms-1 in a time interval of 2s. What is…
- An object at rest starts moving. It covers a distance of 2m in one second. It covers a…
- If a body is moving with uniform velocity in a given direction its acceleration will be…
- Distinguish between speed and velocity. Answer the following
- Distinguish between distance travelled and displacement. Answer the following…
- What are uniform and non-uniform speed? Answer the following
- While mentioning acceleration the time is mentioned two times. Why? Answer the following…
- Extended activity Represent the following motion by a graph. 1. Find the acceleration 2.…
Exercises
Question 1.Uniform circular motion is called continuously accelerated motion because,
A. direction of motion changes continuously
B. speed changes
D. velocity remains the same
D. direction of motion does not change
Answer:
In uniform circular motion, the speed is constant. The direction of motion of a body in uniform circular motion is given by a tangent drawn at the point where the body is. As the direction of motion changes at every instant, the velocity changes continuously. The continuous change in velocity makes it a continuously accelerated motion.
Question 2.
A cricketer hits a sixer. The cricket ball moves up with a velocity of 2 ms-1 and falls down. Its initial velocity while falling down will be
A. 1 ms-1
B. 1 ms-2
C. 0 ms-1
D. 2 ms-1
Answer:
The ball will stop at its maximum height where final velocity will be 0 ms-1 . Then the ball will start falling towards the ground. The initial velocity of fall will be the final velocity of ball when reached maximum height. Thus, initial velocity is 0 ms-1 .
Question 3.
Fill in the blanks with suitable words
S I Unit of acceleration is _____________ .
Answer:
S I Unit of acceleration is ms-2 .
Question 4.
Fill in the blanks with suitable words
Velocity has both speed and _____________ .
Answer:
Velocity has both speed and direction.
Explanation: Velocity is a vector quantity. It has both magnitude and the direction of motion.
Question 5.
Fill in the blanks with suitable words
If an object starts from ‘A’ and comes back to ‘A’, its displacement will be __________ .
Answer:
If an object starts from ‘A’ and comes back to ‘A’, its displacement will be zero.
Explanation: The displacement of an object is the shortest distance between its initial and final position. If the initial position is same as final position, the displacement is zero.
Question 6.
Solve
An object is moving in a circular path of radius 3.5m. If it completes one full cycle, what will be the displacement and what is the distance travelled?
Answer:
Given, radius(r) = 3.5 m
On completing one full cycle, the initial and final position of the object will be same.
Displacement = 0 as initial and final position are same.
Question 7.
Solve
An object changes its velocity from 30 ms-1 to 40 ms-1 in a time interval of 2s. What is its acceleration?
Answer:
Given,
initial velocity(u) = 30 ms-1
final velocity(v) = 40 ms-1
time(t) = 2 s
Thus,
Question 8.
Solve
An object at rest starts moving. It covers a distance of 2m in one second. It covers a further distance of 5 m in two seconds in the same direction. What is its average velocity and acceleration?
Answer:
Given,
The object is at rest, so initial velocity is zero.
⇒u = 0
In one second, distance travelled = 2 m
In next two seconds, distance travelled = 5 m
Total time taken(t) = 1 + 2 = 3 s
Total distance travelled(s) = 2 + 5 = 7 m
As the direction of motion is not changed, so distance = displacement.
Total Displacement = 7 m
Question 9.
Answer the following
If a body is moving with uniform velocity in a given direction its acceleration will be zero. Why?
Answer:
The acceleration of a body is the rate of change of velocity. If the velocity is not changed with time, then the acceleration is constant and is equal to zero. So, for a body moving with uniform velocity, the acceleration is zero.
Question 10.
Answer the following
Distinguish between speed and velocity.
Answer:
Question 11.
Answer the following
Distinguish between distance travelled and displacement.
Answer:
Distance travelled is the length of the actual path travelled by a body.
Displacement is the shortest distance between the initial and final position of the body.
Question 12.
Answer the following
What are uniform and non-uniform speed?
Answer:
If a body does not changes its speed with respect to time, it is said to be moving with uniform speed.
If a body changes its speed with respect to time, it is said to be moving with non-uniform speed.
Question 13.
Answer the following
While mentioning acceleration the time is mentioned two times. Why?
Answer:
The acceleration is the rate of change of velocity with time and the velocity is the rate of change of displacement with time. As both the terms are time dependent, thus with acceleration, time is mentioned twice.
Question 14.
Extended activity
Represent the following motion by a graph.
1. Find the acceleration
2. Find the time taken when the velocity is 35 ms-1.
Answer:
1. 
2. At v = 35 ms-1
a = -1 ms-2
