Question

Q2.The speedometer readings of a car are shown below. Find the acceleration of the car and

its displacement.

Time Speedometer

9:25 a.m. 36 km/h

9:45 a.m. 72 km/h​

Answer 1

Answer:

The Speedometer readings are given below :

Time — Speed

9.25 AM — 36 km/h

9.45 AM — 72 km/h

Let us find :

• Time = 45 - 25 = 20 m = 20 × 60 = 1,200 s
• Initial Speed = 36 km/h = 36×5/18 = 180/18 = 10 m/s
• Final Speed = 72 km/h = 72×5/18 = 360/18 = 20 m/s

So, Acceleration of the car = (v-u)/t

⇒ a = (20-10)/1,200

⇒ a = 10/1,200

⇒ a = 1/120

⇒ a = 0.008 m/s²

Now, Displacement of the car :

Using the second equation of motion -

⇒ s = ut + ½at²

⇒ s = 10*1,200 + ½*0.008*(1,200)²

⇒ s = 12,000 + ½*0.008*1,200*1,200

⇒ s = 12,000 + 600*1,200*0.008

⇒ s = 12,000 + 4.8*1,200

⇒ s = 12,000 + 5,760

⇒ s = 17,760 m

Hence,

• The Acceleration of the car = 0.008 m/s².
• The Displacement of the car = 17,760 m.

Answer 2

Given :-

The speedometer readings of a car are shown below

Time Speedometer

9:25 a.m. 36 km/h

9:45 a.m. 72 km/h​

To Find :-

Acceleration and displacement

Solution :-

Time = 9.45 - 9.25 = 20 min = 20 × 60 = 1200 sec

Initial velocity = 36 × 5/18 = 2 × 5 = 10 m/s

Final velocity = 72 × 5/18 = 4 × 5 = 20 m/s

Now

v = u + at

20 = 10 + a(1200)

20 - 10 = 1200a

10 = 1200a

1 = 120a

1/120 = a

Now

v² - u² = 2as

(20)² - (10)² = 2 × 1/120 × s

400 - 100 = 2/120 × s

300 = 1/60 × s

300 × 60 = s

18000 = s

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