Page 96 - Understanding NCERT Science 09

where u is initial velocity of the object, which moves with
uniform acceleration a for time t, v is its final velocity and s
is the distance it travelled in time t.
• If an object moves in a circular path with uniform speed, its
motion is called uniform circular motion.

Exercises

1. An athlete completes one round of a circular track of diameter
200 m in 40 s. What will be the distance covered and the
displacement at the end of 2 minutes 20 s?
2. Joseph jogs from one end A to the other end B of a straight
300 m road in 2 minutes 30 seconds and then turns around
and jogs 100 m back to point C in another 1 minute. What
are Joseph’s average speeds and velocities in jogging (a)
from A to B and (b) from A to C?
3. Abdul, while driving to school, computes the average speed
–1
for his trip to be 20 km h . On his return trip along the
same route, there is less traffic and the average speed is
30 km h . What is the average speed for Abdul’s trip?
–1
4. A motorboat starting from rest on a lake accelerates in a
–2
straight line at a constant rate of 3.0 m s for 8.0 s. How
far does the boat travel during this time?
5. A driver of a car travelling at 52 km h –1 applies the brakes
Shade the area on the graph that represents the distance
travelled by the car during the period.
(b) Which part of the graph represents uniform motion of
the car?
6. Fig 7.10 shows the distance-time graph of three objects A,B
and C. Study the graph and answer the following questions:

Fig. 7.10

MOTION 85

Rationalised 2023-24