A biker starts a race and crosses the half line in 3 second with speed 54 km/h and
after that he increases his speed uniformally at a rate 7.5 m/s2 and completed the
race in 5 second
(A) Acceleration in the first half of the race is 5 m/s2
(B) He finished the race with speed 108 km/h
(C) Acceleration in the second half of the race is 12.5 m/s2
Choose the correct option.
Answers
Given : A biker starts a race and crosses the half line in 3 second with speed 54 km/h and after that he increases his speed uniformly at a rate 7.5 m/s²and completed the race in 5 second
To Find : Correct option
(A) Acceleration in the first half of the race is 5 m/s2
(B) He finished the race with speed 108 km/h
(C) Acceleration in the second half of the race is 12.5 m/s2
Choose the correct option.
Solution:
Speed = 54 km/hr = 54 * 1000/3600 = 15 m/s
Time = 3 sec
Distance = 15 * 3 = 45 m
increases his speed uniformly at a rate 7.5 m/s2 and completed the
race in 5 second
u = 15 m/s
a = 7.5 m/s²
t = 2 sec
v = u + at
=> v = 15 + 7.5*2 = 30 m/s
30 * 3600 / 1000 = 108 km/hr
d = (1/2) (15 + 30) * 2 = 45 m
Acceleration in the first half of the race is 5 m/s2 INCORRECT
as acceleration is ZERO
He finished the race with speed 108 km/h - CORRECT
Acceleration in the second half of the race is 12.5 m/s² incorrect as its given 7.5 m/s²
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