CBSE Class 9 Science Motion Worksheet Set A

Circular Motion

Uniform circular motion is the motion in which an object moves on a circular path with constant speed. For example: watch, moon revolve around earth etc.

Non uniform circular motion is the motion in which an object is moves on circular path with varying speed. When an object is in circular motion, direction of its velocity keeps on changing. (Image 1)

Speed in the case of circular motion Suppose a body is moving in a circular path of radius r.
Speed (v) = distance / time
= circumstance of circle / time
= 2Πr / t

Uniform circular motion
• When an object moves in a circular path at a constant speed then motion of the object is called uniform circular motion.
• In our everyday life ,we came across many examples of circular motion for example cars going round the circular track and many more .Also earth and other planets revolve around the sun in a roughly circular orbits
• If the speed of motion is constant for a particle moving in a circular motion still the particles accelerates because of constantly changing direction of the velocity.
• If an object moves in a circular path with uniform speed, its motion is called uniform circular motion
• Here in circular motion, we use angular velocity in place of velocity we used while studying linear motion.
• Force which is needed to make body travel in a circular path is called centripetal force.
• We know that the circumference of a circle of radius (r) is given by 2Πr . If the body takes (t) seconds to go once around the circular path of radius ( r ) the velocity ( v) is given by v= 2Πr /t
• One thing we must keep in mind is that uniform linear motion is not accelerated but uniform circular motion is accelerated motion.
• Examples of uniform circular motion are (a) Motion of artificial satellites around the earth (b) Moon, the natural satellite of earth, moves in uniform circular motion round the earth.
(c) Cyclist moving on a circular track with a constant speed exhibits uniform circular motion.

POINTS TO REMEMBER:
• If an object moves in a circular path with uniform speed, its motion is called uniform circular motion.
• Velocity is changing as direction keeps changing.
• Acceleration is constant

Question. See the representation of a park in the map below.Which of these scenes may a visitor entering the park from the entrance see?

Answer : A

Question. When a car turns, its front wheels do not turn by the same amount. In order that the car turn around a common point, the wheel on the side to which the car is turning, turns more than the other. Which of these correctly shows the alignment of a car's wheels when it is turning to its right?

Answer : A

Question. A hunter sees a fish which is swimming in clear water as shown in the figure. To hit the fish, he should take aim adjusting for the fish's motion and ____

(a) exactly at the depth the fish appears to him to be.
(b) a little below where the fish appears to him to be.
(c) a little above where the fish appears to him to be.
(d) at the fish's eye, exactly where it appears to be.

Answer : B

Question. The shortest airline route from Moscow in Russia to Montreal in Canada is likely to be which of these shown on the world map?

(a) A
(b) B
(c) C
(d) D

Answer : D

Question. A truck is carrying a water tank which has two taps on either side as shown in the figure. The taps are opened as the truck starts moving in the circular path at a constant speed. As the truck just completes the circle, the water in the tank runs out completely. What will be the shape of the water trail on the ground if seen from the top?

Answer : B

Question. The unit of distance is metres. The unit of time is seconds. Hence the speed of a person who walks 100 metres in 50 seconds is 100m divided by 50 seconds which is 2 m/s or 2 metres per second.To find out the speed of gas moving through a large gas pipeline, an oil company measures that 10 kg of gas flows every 10 seconds. The mass flow rate is obtained by dividing the distance covered by the time taken to cover it. Then, the mass flow rate in the pipeline is expressed in the unit ---
(a) m/s
(b) kg/s
(c) Kg/m
(d) s/kg

Answer : B

Question. The rate of growth of hair on the human head has been estimated as about 0.44 mm per day. Assuming that this rate is uniform, about what LENGTH of hair (considering just 1 strand) would a normal male adult cut in 20 years?
(a) About 30 cm
(b) About 3 m.
(c) About 30 m.
(d) About 300 m.

Answer : B