Question

Q3 A car moving with a speed of 72kmph applies brakes for 5 seconds. After 5 seconds, these
of the car 18 kmph, Calculate the acceleration of the car.​

Answer 1

✬ Acceleration = –3 m/s² ✬

Explanation:

Given:

• Initial velocity of car is 72 km/h.
• Time given is 5 seconds.
• Final velocity of car is 18 km/h.

To Find:

• What is acceleration of car ?

Formula to be used:

• v = u + at (first law of motion)

Solution: First of all convert the km/h to m/s. To convert multiply the speed by 5/18.

➨ Initial velocity = 72 × 5/18 = 4 × 5 = 20 m/s.

➨ Final velocity = 18 × 5/18 = 1 × 5 = 5 m/s.

Now we have

• u = 20 m/s.
• v = 5 m/s.
• t = 5 s

Putting all the values on formula

$\implies{\rm }$ v = u + at

$\implies{\rm }$ 5 = 20 + a × 5

$\implies{\rm }$ 5 – 20 = 5a

$\implies{\rm }$ –15 = 5a

$\implies{\rm }$ –15/5 = a

$\implies{\rm }$ –3 = a

Hence, the acceleration of car is –3 m/s².

• The rate of change of velocity is called acceleration. It is denoted by a.

• The velocity at which motion starts is termed as initial velocity. It is denote by u.

• The last velocity of an object after a period of time. It is denoted by v.

• v = ut + 1/2at² ( Second law of motion)

• v² = u² + 2as ( Third law of motion )

Answer 2

$\sf{\pink{\underline{\underline{\purple{GIVEN:-}}}}}$

• A car is moving with a speed = 72 km/h

• It applies brakes for 5s .

• After 5s the speed of the car = 18 km/h

$\sf{\pink{\underline{\underline{\purple{TO\:FIND:-}}}}}$

• Acceleration of the car .

$\sf{\pink{\underline{\underline{\purple{SOLUTION:-}}}}}$

$\orange\star\:\bf{\gray{\boxed{\pink{\boxed{\red{v\:=\:u\:+\:at\:}}}}}}$

According to the question,

• Initial velocity (u) = 72 km/h = 20 m/s

• Time (t) = 5 s

• Final velocity (v) = 18 km/h = 5 m/s

$\rm{\implies\:5\:=\:20\:+\:a\times{5}\:}$

$\rm{\implies\:a\:=\:\dfrac{5\:-\:20}{5}\:}$

$\rm{\implies\:a\:=\:\dfrac{-15}{5}\:}$

$\rm\green{\implies\:a\:=\:-3\:m/s^2}$

[Note :- -ve sign indicates that the car is in deaccelerating motion .]

$\rm\pink{\therefore}$ The acceleration of the car is “ 3 m/s² ”