Question

A car of mass 1200g is brought to rest by a uniform force of 300 N in 80 sec
What was the speed of the car

Answer 1

Answer:

Explanation:

Solution,

Mass of the car, m = 1200 g = 1.2 kg

Final speed of car, v = 0 (As car was brought to rest)

Time taken by car, t = 80 seconds

To Find,

Speed of car i.e initial speed, u = ??

At, 1st we will find out acceleration,

We know that,

⇒ F = ma

⇒ a = F/m

⇒ a = 300/1.2

⇒ a = 250 m/s²

Here, the acceleration is 250 m/s².

According to the 1st equation of motion,

We know that

v = u + at

So, putting all the values, we get

⇒ v = u + at

⇒ 0 = u + 250 × 80

⇒ u = 250 × 80

⇒ u = 20000 m/s²

Hence. the speed of the car was 20000 m/s².

Answer 2

Given :

Mass , m = 1200 g = 1.2 kg

Final speed , v = 0 m/s

Force , F = 300 N

Time , T = 80 sec

Speed , v = ? m/s

A/c to Newton second law ,

• F = ma

⇒ 300 = 1.2 (a)

⇒ a = 250 m/s²

Now using first equation of Motion ,

• v = u + at

⇒ 0 = u + 250(80)

⇒ u = -20,000

But speed can't be negative .

Hence the speed of the car is 20,000 m/s