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

Given :

• Initial velocity, u = 90 km/h = 25 m/s
• Final velocity, v = 0 m/s
• Time, t = 5 seconds
• Mass, m = 200 kg

To find :

• Force exerted, F

According to the question,

➞ v = u + at

Where,

• v = Final velocity
• u = Initial velocity
• a = Acceleration
• t = Time

➞ 0 = 25 + a × 5

➞ 0 - 25 = 5a

➞- 25 = 5a

➞ - 25 ÷ 5 = a

➞ - 5 = a

So,the acceleration is - 5 m/s².

Note : Negative signs means retardation.

➞ Force = Mass × Acceleration

Or,

➞ F = ma

➞ F = 200 × (-5)

➞ F = - 1000 N

So,the force exerted is - 1000 Newton.

Note : Negative signs means that the force is acting on opposite direction.

Answer 2

Answer:

Given :-

• A motorcycle is moving with a velocity of 90 km/h and its takes 5 seconds to stop after the brakes are applied and its mass along the rider is 200 kg.

To Find :-

• How much force exerted by the brakes on the motorcycle.

Formula Used :-

❶ To find acceleration we know that,

✦ a = v - u/t ✦

where,

• v = Final velocity
• u = Initial velocity
• a = Acceleration
• t = Time

❷ To find force we know that,

❖ F = ma ❖

where,

• F = Force
• m = Mass
• a = Acceleration

Solution :-

❶ First we have to find the acceleration,

Given :

• v = 0 m/s
• u = 90 km/h = 90 × 5 ÷ 18 m/s = 25 m/s
• t = 5 seconds

According to the question by using the formula we get,

⇒ a = 0 - 25/5

⇒a = - 25/5

➠ a = - 5 m/s²

Hence, acceleration is - 5 m/s² .

❷ Now we have to find the force,

We get,

• Mass = 200 kg
• Acceleration = - 5 m/s

According to the question by using the formula we get,

↦ F = 200 × - 5

➥ F = - 1000 N

∴ The force exerted by the brakes on the motorcycle is - 1000 N .