Question

A car of mass 2000 kg is moving with a speed of 20
m/s. To stop it brakes are applied. If the retarding
force is 2000 N, the time required to stop the car will
be :
(a) 5 sec (b) 10 sec (c) 15 sec (d) 20 sec.​

Answer 1

Answer:

d) 20sec

Step-by-step explanation:

given,

mass=2000kg

u= 20m/s

v= 0m/s

force= 2000N

force= mass×acceleration

2000= 2000×a

1=a

according to 1st eq. of motion

v=u+at

0=20+(-1)t. (-1 becaue of retardation)

-20=-t

20=t

.......666......

Answer 2

Answer :

›»› The Time taken to stop the car = 20 sec

Given :

• Mass of car (m) = 2000 kg
• Initial velocity of car (u) = 20 m/s
• Final velocity of car (v) = 0 m/s
• Force (F) = -2000 N

To Calculate :

• Time taken to stop the car (t) = ?

How To Calculate ?

❒ Here in this question we have to find Time taken to stop the car. So, firstly we need to calculate the Acceleration of car by using the second law of Newton, after that we will find Time taken of car to stop by using the first equation of motion.

Calculation :

‡ From Second law of Newton

⇒ F = ma

⇒ -2000 = 2000 × a

⇒ -2000 = 2000a

⇒ a = -2000/2000

⇒ a = -1 m/s²

【NOTE : -ve sign indicates retardation of car.】

Now, we have three elements that used in formula, Final velocity, Initial velocity and Acceleration of car$.$

• Final velocity of car (v) = 0 m/s
• Initial velocity of car (u) = 20 m/s
• Acceleration of car (a) = 1 m/s²

And we need to find Time taken by car to stop.

† From first equation of motion

⇛ v = u + at

⇛ 0 = 20 + -1 × t

⇛ 0 - 20 = -t

⇛ -20 = -t

⇛ 20 = t

⇛ t = 20

║Hence, the time taken to stop the car will be 20 seconds.║