Question

18.A bus decreases its speed from 90km/hr to 36 km/hr in 10 seconds. Find the acceleration of the bus in m/s2.

1.5

-1.5

5.4

-5.4

​

Answer 1

Given :

• Initial Velocity (u) = 90 km/hr

• Final Velocity (v) = 36 km/hr

• Time (t) = 10 seconds

To Find :

• Acceleration of the bus

Solution :

First of all let's convert given velocities into m/s

• 90 km/ hr

→ 90 × 5/18

→ 5 × 5

→ 25 m/s

• 36 km/hr

→ 36 × 5/18

→ 2 × 5

→ 10 m/s

Now,

★ Acceleration = Final Velocity - Initial Velocity/Time taken

★ a = v - u/t

→ a = 10 - 25/10

→ a = -15/10

→ a = -1.5 m/s²

$\therefore$ Acceleration of the bus is -1.5 m/s²

Since the speed of the bus is decreasing, therefore the value of the acceleration is in negative.

Answer 2

Given :-

• Initial velocity = 90km/h =90×5/18=25m/s

• Final velocity =38km/h =38×5/18=10m/s

• Time taken =10s.

To Find:-

• Acceleration of bus.

Solution :-

By using 1st equation of motion

➦ v=u+at

➭ 10=25+a ×10

➭ 10×a = 10-25

➭ a = -15/10

➭ a = -1.5m/s²

∴ The acceleration of car is -1.5m/s²