Question

A car of mass 1200 kg moving with a velocity of 72km/h is stopped in 5s on applying breaks. Calculate the retardation and the retarding force.

Answer 1

Explanation:

Velocity of the car = 72 km/hr

converting it into m/s

72x 1000

3600

20 m/s is its velocity

mass of the car = 800 kg

equation for force=mass multiplied by acceleration

so we need to find acceleration first

time taken to stop the car = 10 min

t = 10 min = 10 x 60 = 600 s

a=(v-u)/t

a=(0-20)/600

a=-20/600

a=-1/30

now we get

f=800 x -1

30

f=26.6N

Answer 2

Given :-

A car of masss 1200 kg moving with a velocity of 72 km/hr is stopped in 5 seconds on applying brakes

Required to find :-

• Retardation ?

• Retardation force ?

Formulae used :-

$\huge{\dagger{\tt{\bf{ a = \dfrac{ v - u }{ t } }}}}$

$\huge\overline{\underline{\rm{\bf{ F = ma }}}}$

Solution :-

Given information :-

A car of mass 1200 kg moving with a velocity of 72 km/hr is stopped in 5 seconds on applying brakes

we need to find the retardation and retardation force

From the given information we can conclude that ;

• Mass of the car = 1, 200 kg

• Initial velocity of the car = 72 km/hr

• Final velocity of the car = 0 km/hr

Here, we need to convert the final and initial velocity of the car from km/hr into m/s

So,

• 1 km/hr = 5/18 m/s

72 km/hr = ? m/s

=> 72 x 5/18

=> 4 x 5

=> 20 m/s

72km/hr = 20 m/s

However,

0 km/hr = 0 m/s

This implies ;

• Initial velocity of the car = 20 m/s

• Final velocity of the car = 0 m/s

• Time = 5 seconds

Using the formula ;

$\huge{\dagger{\tt{\bf{ a = \dfrac{ v - u }{ t } }}}}$

So,

Acceleration = 0 - 20 / 5

Acceleration = - 20 / 5

Acceleration = - 4 m/s²

( Since, Negative acceleration is retardation )

Hence,

• Retardation = - 4 m/s²

Now, we need to find the retardation force ;

Using the formula ;

$\huge\overline{\underline{\rm{\bf{ F = ma }}}}$

Force = 1, 200 kg x - 4 m/s

Force = - 4, 800 kg*m/s²

( Since, 1 kg*m/s² = 1 N )

Force = - 4, 800 N

Therefore,

• Retardation force = - 4, 800 N