Question

If a body is moving with a velocity 36 kmph after 4s it’s velocity is 72 kmph then find displacement of a body during this 4s.

Answer 1

Answer:

• Initial Velocity (u) = 36 km/h = 10 m/s
• Final Velocity (v) = 72 km/h = 20 m/s
• Time taken (t) = 4 s
• Displacement (s) = ?

• Using the First equation of Motion :

⇒ v = u + at

⇒ 20 = 10 + (a × 4)

⇒ 20 - 10 = a × 4

⇒ 10 = a × 4

⇒ 10 / 4 = a

⇒ a = 2.5 m/s²

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• Using the Third equation of Motion :

⇢ v² - u² = 2as

⇢ (20)² - (10)² = 2 × 2.5 × s

⇢ (20 + 10)(20 - 10) = 5 × s

• (a² - b²) = (a + b)(a - b)

⇢ 30 × 10 = 5 × s

⇢ (30 × 10) / 5 = s

⇢ 30 × 2 = s

⇢ s = 60 m

∴ Displacement of body during 4s is 60 m.

Answer 2

☯ Displacement = 60m

Given ,

• Initial velocity (u) = 36 km/h
• Final velocity (v) = 72 km/h
• Time taken to change velocity = 4s

We need to find ,

• Displacement of body = ?

Using third equation of motion ,

♦ v² - u² = 2as

Since , in the question they didn't give the acceleration of the body . So , first we need to find the acceleration of the body using ,

♦ a = v - u/t

Also , all units should be in S.I. units. So ,

• 72km/h = 20m/s
• 36km/h = 10m/s

So , now

➠ a = 20 - 10/4

➠ a = 10/4

➠ a = 5/2

➠ Acceleration = 2.5 m/s²

Now finding displacement using third equation of motion .

➳ v² - u² = 2as

➳ 20² - 10² = 2 × ( 2.5 ) × ( s )

➳ 400 - 100 = 5s

➳ 300 = 5s

➳ s = 300/5

➳ Displacement = 60m