Question

A mobile starts with a speed of 250m / s and begins to decelerate at a rate of 3m / s². How fast is it after 45s?

Answer 1

`\large{ \underline{ \underline{ \bf{ \purple{Given}}}}}`

• Speed of the mobile = 250 m/s
• It starts decelerating at a rate of 3 m/s²
• Time travelled = 45s

`\large{ \underline{ \underline{ \bf{ \green{To \: find}}}}}`

• Velocity of mobile after 45 seconds

`\large{ \underline{ \underline{ \red{ \bf{Now, \: What \: to \: do?}}}}}`

We can solve the above question using the three equations of motion which are:-

• v = u + at
• s = ut + 1/2 at²
• v² = u² + 2as

So, Here a is acceleration of the body, u is the initial velocity, v is the final velocity, t is the time taken and s is the displacement of the body.

`\large{ \bf{ \underline{ \underline{ \orange{Solution:}}}}}`

We are provided with,

• u = 250 m/s
• a = -3 m/s²
• t = 45 s

By using 1st equation of motion,

⇛ v = u + at

⇛ v = 250 + (-3)45

⇛ v = 250 - 135 m/s

⇛ v = 115 m/s

✤ Final velocity of mobile = 115 m/s

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