Question

A train start's from rest, travelling with uniform acceleration reached 90 km/h within 5s. then:
(a) what is the initial velocity
(b)calculate acceleration​

Answer 1

Answer:

$\bigstar{\bold{Initial\:velocity=0\:km/hr}}$

$\bigstar{\bold{Acceleration=5\:m/s^{2} }}$

Explanation:

$\Large{\underline{\underline{\bf{Given:}}}}$

• The train starts from rest
• Final velocity = 90 km/hr
• Time taken = 5 s

$\Large{\underline{\underline{\bf{To\:Find:}}}}$

• The initial velocity
• Acceleration

$\Large{\underline{\underline{\bf{Solution:}}}}$

Initial velocity:

→ Here we have to find the initial velocity of the body.

→ According to the question, the train starts from rest so the velocity at the start is 0.

→ Hence the initial velocity of the train is 0 km/hr

$\boxed{\bold{Initial\:velocity=0\:km/hr}}$

Acceleration:

→ Now we have to find the acceleration of the train within the time interval of 5 s.

→ By the first equation of motion, we know that

  v = u + at

  where v = final velocity

  u = initial velocity

  a = acceleration

  t = time

→ Here we have to convert the velocity from km/hr to m/s

  90 km/hr = 90 × 5/18 = 25 m/s

→ Hence the final velocity of the train is 25 m/s

→ Substituting it in the above equation we get,

  25 = 0 + a × 5

  5a = 25

    a = 25/5

    a = 5 m/s²

→ Hence acceleration of the train is 5 m/s²

$\boxed{\bold{Acceleration=5\:m/s^{2} }}$

$\Large{\underline{\underline{\bf{Notes:}}}}$

→ The three equations of motion are:

• v = u + at
• s = ut + 1/2 × a × t²
• v² - u² = 2as

Answer 2

Answer:

initial velcity is 0

90 km/h=90x5/18=25m/s

v=u+at

25=0+ax5

a=5m/s^2...