Question

A train is moving on a railway track at a speed of 100 km/hr. The brakes are applied and after 40 s the speed decreases by 10 %. The detardation of the train is proportional to the velocity of the train. Determine the velocity of the train in km/hr at the time period of 120 s.

Answer 1

Answer:

The speed after 120s will be 70 km/h

Explanation:

We need to calculate the retardation in 40s.

The speed decreases by 10%.

10% of 100km/h = 10/100 × 100 =

10 km/h

We convert the time to hours = 40/3600 = 1/90 hours

Retardation = change in speed / time

= 10 × 90 = 900 km/h²

Now given:

u = 100 km/h

t = 120s = 120/3600 = 1/30 hrs

a = 900km/h²

We will apply kinematics equation to get the final velocity.

V = u - at

Substituting we have :

V = 100 - 900 × 1/30

V = 100 - 30 = 70 km/h

After 120 seconds the speed will be 70 km/h