Question

Find the time taken if the speed of a train increased rom 72km/h to 90km/h for 234km

Answer 1

Answer:

Explanation:

s = s₀ + v₀t + ½at²

Let s₀ = 0 be the position in km where acceleration starts,

Let t be in hours

a = (90 - 72) / t = 18/t  km/hr²

234 = 0 + 72t + ½(18/t)t²

234 = 72t + 9t

234 = 81t

t = 2.88888... ≈ 2.89 hr

Answer 2

Answer:

2.89 hours

Explanation:

given :

Vo = 72 km/h

Vt = 90 km/h

S = 234 km

find : the time taken (t) = ?

solution :

2.a.s = Vt² - Vo²

2.a.(234) = 90²- 72²

468.a = 8100 - 5184

= 2916

a = 2916/468 = 6.23 km/h²

so,

t = (Vt-Vo) /a

= (90-72)/ 6.23

= 18/ 6.23

= 2.89 hours