Question

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A car travelling at 110 km/h decelerates for 4.5 seconds to a final velocity of 45 km/h. Calculate the deceleration of the car​

Answer 1

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Answer 2

Given :

A car travelling at 110 km/h decelerates for 4.5 seconds to a final velocity of 45 km/h. Calculate the deceleration of the car

Need to Find : The deceleration of the car

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★ Cᴏɴᴄᴇᴘᴛ :

According to the question, here we are given that the initial velocity of the car is 110 km/h and it decelerates for 4.5 sec to reach the final velocity which is 45 km/h.

Now, we need to use the first equation of motion to get the deceleration. Putting all the required values we can find the acceleration and from there we need to change into deceleration by putting the -ve sign in front of the value.

★ Sᴏʟᴜᴛɪᴏɴ :

Given Data

Initial Velocity (u) = 110 km/h

As we can see that the initial vel is in km/h instead of m/sec. So, let's convert km/h into m/sec

Conversion : 1 km/h = 5/18 m/sec

Hence, 110 km/h = 110 × 5/18 m/sec = 55 × 5/9 = 30.5 m/sec

Final Velocity (v) = 45 km/h

Again, the final vel is in km/h instead of m/sec. So, let's convert km/h into m/sec

Conversion : 1 km/h = 5/18 m/sec

Hence, 45 km/h = 45 × 5/18 m/sec = 25/2 = 12.5 m/sec

Time (t) = 4.5 sec

Calculation Begins

According to the first equation of motion we get to know that the ingredients are initial velocity, final velocity, time and acceleration. All the three components are given leaving the acceleration.

So, the equation is ⤵

★ v = u + at ★

Here, a refers acceleration

12.5 = 30.5 + a(4.5)

30.5 - 12.5 = -4.5a

-4.5a = 18

a = -18/4.5

a = -4

As the acceleration is -4.5

So, adding -ve sign in front of the value we get deceleration

Deceleration = -(-4) = 4

❒ Hence, the deceleration of the car is 4 m/sec