Question

A motorcar is moving with a velocity of 108 km/h and it

takes 4 s to stop after the brakes are applied. Calculate the

force exerted by the brakes on the motorcar​

Answer 1

Correct Question :-

A motorcar is moving with a velocity of 108 km/h and it takes 4 s to stop after the brakes are applied. Calculate the force exerted by the brakes on the motorcar if its mass along with the passengers is 1000 kg.

Given :

• Initial velocity, u = 108 km/h

• Final velocity, v = 0 m/s

• Time, t = 4 seconds

• Mass (m) = 1000 kg

To find :

• Force exerted by the brakes on the motorcar, F

According to the question,

By using Newtons first equation of motion we will find acceleration then by using F = ma,

Note : We have to convert 108 km/h into m/s. So, it will be 30 m/s.

➞ v = u + at

Where,

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

➞ Substituting the values,

➞ 0 = 30 + a × 4

➞ 0 - 30 = 4a

➞ - 30 = 4a

➞ - 30 ÷ 4 = a

➞ - 7.5 = a

So,the acceleration is - 7.5 m/s².

Note : Negative signs means retardation.

Now,

➞ Force = Mass × Acceleration

Or,

➞ F = ma

➞ Substituting the values,

➞ F = 1000 × (-7.5)

➞ F = - 7500 N

So,the force exerted by the brakes on the motorcar is - 7500 Newton.

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

Answer 2

Answer:

$\huge \bf \: Answer$

Concept :- Here, is a motorcar whose velocity is given and time is given and we have to find the force exerted. And mass 1000 kg .

We must find the acceleration first

$\bf \: v \: = u + at$

$\sf \: 0 = 30 + a \times 4$

$\sf \: 0 - 30 = 4a$

$\sf \: - 30 = 4a$

$\sf \: a = \dfrac{ - 30}{4}$

$\sf \: a \: = - 7.5 \: mps$

Now,

Finding force

$\huge \tt \: f \: = ma$

F = 1000 × -7.5

F = -7500 N