Question

a train starts from rest and accelerates uniformly for 30 seconds to acquire a velocity of 108 kilometre per hour. it travels with this velocity for 20 min. the driver now applies brakes and the train retards uniformly to stop after 20 sec. find the total distance covered by the train.

Answer 1

So, total distance travelled = S1 + S2 + S3

D = 450 + 36000 + 300

D = 36750 m = 36.75 km

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Answer 2

Explanation:

Let S1 ,S2 and S3 is distance travelled

Fir S1,

v = 108 km/h

= 108 × 5/18

= 30 m/s

t = 30 s

a = 30/30

= 1 m/s²

so,

S1 = ½ × 1 × 30 × 30

S1 = 450 m

for S2,

u = 30 m/s(constant)

so,

a = 0

t = 20 min

= 1200 s

S2 = 1200 × 30

S2 = 36000 m

For S3,

u = 30 m/s

v = 0 m/s

t = 20 s

a = -30/20

a = -1.5 m/s²

so,

S3 = -u²/2a

= -900/2(-1.5)

= 900/3

S3 = 300 m

Now,

total distance covered = S1 + S1 + S3

= 450 + 36000 + 300

= 36750 m

= 36.75 Km