science
Grade-9
Easy
Question
A car moving at a velocity of 5 m/s accelerates to 25 m/s while covering a distance of 1.8 km. The time it takes to cover that distance is ___ seconds.
Hint:
120 s
The correct answer is: 120
Given that,
The initial velocity, u = 5 m/s
The final velocity, v = 25 m/s
The distance covered, s = 1.8 km = 1800 m
On using the third equation of motion we get,
v2 = u2 + 2as
Or, (25)2 = (5)2 + 2 x a x 1800
Or, 625 = 25 + 3600 a
Or, 3600 a = 625 – 25
Or, 3600 a = 600
Or, a = 600/ 3600 = 1/6 m/s2
Therefore, the acceleration of the car is 1/6 m/s2.
On using the first equation of motion we get,
v = u + at
Or, 25 = 5 + (1/6) x t
Or, t/6 = 20
Or, t = 20 x 6
Or, t = 120 s
Therefore, the time taken by the car is 120 s.
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