Question

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The above figure(in attachment) shows a situation just before a collision. A lorry of mass 20,000 kg is travelling at 20 m/s towards a car of mass 900 kg travelling at 30 m/s towards the
lorry.

i) What is the momentum of the lorry before collision?

ii) What is the momentum of the car before collision?

iii) What is the total momentum after the collision?

ᴅᴏɴ'ᴛ sᴘᴀᴍ ​

Answer 1

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Given :

• $Mass_{1}$ $\rightarrow$ 20,000kg

• $u_{1}$ $\rightarrow$ 20m/s

• $Mass_{2}$ $\rightarrow$ 90kg

• $u_{2}$ $\rightarrow$ 30m/s

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To Find:

$\rightarrow$i) What is the momentum of the lorry before collision?

$\rightarrow$(ii) What is the momentum of the car before collision?

$\rightarrow$ iii) What is the total momentum after the collision?

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Solution :

Let's the lorry be moving from left to right .By convention left to right is taken as the positive direction and thus right to left is negative direction..

$\rightarrow$ If symbol $\color{red} {m}$and $\color{red} {u}$ represent the mass and Initial velocity of the vehicles. So,

(1) $Mass_{1}$ $\rightarrow$ 20,000 kg

$u_{1}$ $\rightarrow$ +20m$s^{-1}$ and

(2) $Mass_{2}$ $\rightarrow$ 900kg

$u_{2}$ $\rightarrow$ - 30m/$s^{-1}$

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$\color{red} {Momentum}$ = $\color{green} {mass\:×\: velocity}$

$\rightarrow$ $\color{red} {p}$ = $\color{green} {m×v}$

$\rightarrow$ Here, $\color{red} {p\:=\: Momentum\: m\:=\:mass\:and\:v\:=\: velocity}$

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(a) Momentum of lorry before collision :

$\sf\huge\implies$ $\color{red} {p\:. =\: m\: v}$

$\sf\huge\implies$ p = 20,000 × 20

$\sf\huge\implies$ 400,000 kg m $s^{-1}$

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(b) Momentum of car before collision :

$\sf\huge\implies$ $\color{red} {p\:. =\: m\: v}$

$\sf\huge\implies$ p = 900 × ( -30)

$\sf\huge\implies$ -27,000 kg m $s^{-1}$

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(c) Total momentum after collision :

$\sf\huge\implies$ ( $m_{1}$ + $m_{2}$ ) × v

$\sf\huge\implies$ ( 20,000 + 400,000 ) kg × v m$s^{-1}$

$\sf\huge\implies$ 420,000kg m$^s{-1}$

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Final answers :

• 400,000 kg m $s^{-1}$

• -27,000 kg m $s^{-1}$

• 420,000kg m$^s{-1}$

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Note : swipe right to left to see full answer .

Answer 2

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Explanation: