Question

A car is moving with uniform velocity of 60 m/s. It is stopped in 3 sec by applying a force of 2580 N through its brakes. Calculate the mass of the car​

Answer 1

Given :

Initial velocity of the car, u= 60 m/s

Final velocity of the car, v = 0

Time taken, t = 3 sec

Force, F = 2580 N

To find :

Mass of the car

Solution :

1st of all we have to find accerlation,

so, using first equation of motion .i.e.,

➠ v = u + at

Substituting all the given values,

➠ 0 = 60 + (a)(3)

➠ 0 = 60 + 3a

➠ 3a = - 60

➠ a = - 60/3

➠ a = - 20 m/s²

Remember !

If the speed is decreasing with time then accerlation is negative. negative accerlation is called retardation.

Now, using Newton's 2nd law of motion

the rate of change of linear Momentum of a body with time is proportional to the net external force acting on it. .i.e.,

➠ F = ma

➠ 2580 = (m)(20)

➠ m = 2580/20

➠ m = 129kg${.}$

thus, the mass of a car is 129kg.

Answer 2

Given :

• Initial velocity (u) = 60 m/s
• Final velocity (v) = 0 m/s
• Time (t) = 3 seconds
• Force (F) = 2580 N

To find :

• Mass of the car

According to the question,

By using Newton's first equation of motion,

⇒ v = u + at

Where,

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

⇒ Substituting the values,

⇒ 0 = 60 + a × 3

⇒ 0 - 60 = 3a

⇒ - 60 = 3a

⇒ - 60 ÷ 3 = a

⇒ - 20 = a

So,the retardation is 20 m/s².

Now,

We know that :

⇒ Force = Mass × Acceleration

⇒ F = ma

⇒ Substituting the values,

⇒ 2580 = m × 20

⇒ m = 2580 ÷ 20

⇒ m = 129

So,the mass of the car is 129 kg.

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