Question

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?
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?
Abdul, while driving to school, computes the average speed 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 hl. What is the average speed for Abdul's trip?
A motorboat starting from rest on a lake accelerates in a straigh
line at a constant rate of 3.0 m s2 for 8.0 s. How far does th
boat travel during this time?​

Answer 1

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Given, Diameter (d) of the track = 200m

Time taken for 1 round of the track = 40s (t)

Distance travelled in 1 round (s) = circumference of track

= 2π r

= πd

= π x 200

(s) = 200π m

Hence, speed of athlete along the track (V) = s/t = 200π/40

= 5π m/sec

Time interval = 2 minutes 20 sec (Given)

= 140 seconds

∴ distance travelled in 140 sec is given by s = v x t

= 5π x 140

= 5 x 22/7 x 140

= 2200 m

The no of revolutions completed = 2200m/200π.

= 2200/(200x22/7) = 3.5

Athlete has completed 3.5 revolutions.

∴ Displacement of athlete = diameter of track = 200m.

Answer 2

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