Question

7. A motorcycle is moving with a velocity of 90 km h^-1 and it takes 5 seconds to stop after the brakes are
applied. Calculate the force exerted by the brakes on the motorcycle if its mass along with the rider is 200 kg. ​

Answer 1

A N S W E R :

• The force (F) exerted by the brakes on the motorcycle is 1000 N.

Given :

• Initial velocity (u) = 90 km/hr
• Final velocity (v) = 0 m/s
• Time interval (t) = 5 seconds
• Mass of motorcycle along with the rider (m) = 200 kg.

To Find :

• The force (F) exerted by the brakes on the motorcycle = ?

Solution :

First we have to convert initial velocity from km/hr to m/s :

⇒Initial velocity (u) = 90 km/hr

⇒Initial velocity (u) = 90 × 5/18 m/s

⇒Initial velocity (u) = 5 × 5 m/s

⇒Initial velocity (u) = 25 m/s

• Hence,the initial velocity of the motorcycle is 25 m/s.

Now, we need to find the acceleration,for calculating acceleration we will use the first equation of motion :

→ v = u + at

→ 0 = 25 + a × 5

→ 0 - 25 = 5a

→ -25 = 5a

→ a = -25 ÷ 5

→ a = -5 m/s²

• Hence,the acceleration of the motorcycle is 5 m/s² beacuse negative sign indicates retardation.

Let's calculate the force exerted by the brakes on the motorcycle :

⇢Force = mass × acceleration

⇢Force = 200 × 5

⇢Force = 1000 N

• Hence,the force exerted by the brakes on the motorcycle is 1000 N.