# Class 9 Physics Kinematics 7. What is a SI Unit of Velocity.a) \mathrm{Nm} b) \mathrm{ms}^{-1} C) \mathrm{ms}^{-2}

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##### 7. What is a SI Unit of Velocity.a) \mathrm{Nm} b) \mathrm{ms}^{-1} C) \mathrm{ms}^{-2}

EXAMPLE 2.4 A car starts from rest. Its velocity becomes 20 \mathrm{~ms} in 8 \mathrm{~s} . Find its acceleration.

b) Why gravity is taken negative for an object moving in upward direction?

b) How represent vector quantities are represented graphically?

iv.If an object is moving with constant speed then its distance-time graph will be a straight line.(a) along time-axis(b) along distance-axis(c) parallel to time-axis(d) inclined to time-axis

EXAMPLE 2.12A bicycle accelerates at 1 \mathrm{~ms}^{-2} from an initial velocity of 4 \mathrm{~ms}^{-1} for 10 \mathrm{~s} . Find the distance moved by it during this interval of time.

2.5 Can a body moving at a constant speed have acceleration?

vi. The speed-time graph of a car is shown in the figure which of the following statement is true?(a) car has an acceleration of 1.5 \mathrm{~m}^{-2} (b) car has constant speed of 7.5 \mathrm{~ms}^{-1} (c) distance travelled by the car is 75 \mathrm{~m} (d) average speed of the car is 15 \mathrm{~ms}^{-1} v\left(m s^{-1}\right)

2.8 A cricket ball is hit vertically upwards and returns to ground 6 \mathrm{~s} later. Calculate (i) maximum height reached by the ball (ii) initial velocity of the ball.

e) A ball falls down from top of height of 70 \mathrm{~m} . How much time the ball will take to reach the ground.

d) If a body is thrown up ward with vertical velocity 50 \mathrm{~ms}^{-1} . Calculate maximum height which body can reach.

1. Scalar Quantities have . and suitable unit.a) magnitudeb) directionc) both a and b

2.3 Differentiate between the following:(iv) Speed and velocity.

2.2 Explain translatory motion and give examples of various types of translatory motion.

EXAMPLE 2.10A car travelling at 10 \mathrm{~ms}^{-1} accelerates uniformly at 2 \mathrm{~ms}^{-2} . Calculate its velocity after 5 \mathrm{~s} .

EXAMPLE 2.15A boy throws a ball vertically up. It returns to the ground after 5 seconds. Find(a) the maximum height reached by the ball.(b) the velocity with which the ball is thrown up.

Worked Example 7A ball is thrown vertically upward with velocity of 12 \mathrm{ms}^{-1} . The ball will be slowing down due to pull of Earths gravity on it and will return back to Earth.Find out the time the ball will take to reach the maximum height.

a) A bus is moving on a road with 15 \mathrm{~ms}^{-1} and it accelerates at 5 \mathrm{~ms}^{-2} . Find the final velocity of bus after 6 seconds.

2.7 Sketch a distance-time graph for a body starting from rest. How will you determine the speed of a body from this graph?

2.3 Differentiate between the following:(v)Linear and random motion.

xi. A train is moving at a speed of 36 \mathrm{kmh}^{-1} . Its speed expressed in \mathrm{ms}^{-1} is:(a) 10 \mathrm{~ms}^{-1} (b) 20 \mathrm{~ms}^{-1} (c) 25 \mathrm{~ms}^{-1} (d) 30 \mathrm{~ms}^{-1}

5. Distance is a quantity.a) Vectorb) Scalarc) both a and b

EXAMPLE 2.5 Find the retardation produced when a car moving at a velocity of 30 \mathrm{~ms}^{-1} slows down uniformly to 15 \mathrm{~ms}^{-1} in 5 \mathrm{~s} .

iii. Which of the following is a vector quantity?(a) speed(b) distance(c) displacement (d) power

EXAMPLE 2.6 Figure 2.21 shows the distance-time graph of a moving car. From the graph find(a) the distance car has traveled.(b) the speed during the first five seconds.(c) average speed of the car.(d) speed during the last 5 seconds.Figure 2.21: Distance-time graph of a car in example 2.6

8. Shortest distance between two points is calleda) distanceb) speedc) displacement

2.5 A car moves with uniform velocity of 40 \mathrm{~ms}^{\mathrm{w} 1} for 5 \mathrm{~s} . It comes to rest in the next 10 \mathrm{~s} with uniform deceleration. Find (i) deceleration (ii) total distance travelled by the car.