Question

a moving train is bought to rest within 20 seconds by applying brakes.Find the initial velocity (u) if the retardation due to break is 1.5 metre per second square​

Answer 1

GiveN :

• Time interval (t) = 20 s
• Final velocity (v) = 0 m/s
• Retardation (a) = - 1.5 m/s²

To FinD :

• Initial velocity (u)

SolutioN :

Use 1st equation of Kinematics :

➾ v = u + at

➜ 0 = u + 20 * - 1.5

➜ 0 = u - 30

➜ u = 30 m/s

➭ Initial velocity of train is 30 m/s

Answer 2

Given :

• Final velocity of Train, v = 0
• Time for which it moved after applying brakes, t = 20 s
• Retardation due to brakes = 1.5 m/s⁻² ; therefore, acceleration = -1.5 ms⁻²

To find :

• Initial velocity of Train, u = ?

Formula required :

• First equation of motion

      v = u + a t

[ where v is final velocity, u is initial velocity, a is acceleration and t is time taken ]

Calculation :

Using first equation of motion

→ v = u + a t

→ 0 = u + (-1.5) (20)

→ 0 = u - 30

→ u = 30 ms⁻¹

Therefore,

• Initial velocity of Train is 30 ms⁻¹.

Three equations of motion :

• First equation

     v = u + a t

• Second equation

     s = u t + 1/2 a t²

• Third equation

     2 a s = v² - u²

[ Where v is final velocity, u is initial velocity, a is acceleration, t is time taken and s is distance covered by the body ]