Question

Two objects of masses 1kg and 2kg moving with a velocities 2 m/s and 4m/s, respectively. They collide and after collision first object moves at a velocity 3m/s, then velocity of second object is ?
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Answer 1

Given :

• Mass of 1st object = 1kg
• Mass of second object = 2kg
• initial Velocity of first object = 2m/s
• initial Velocity of other object = 4m/s
• Final velocity of first object = 3m/s

To Find :

The Velocity of second object, if they coolide with each other.

Law To Be used :

We will here use the law of Conservation of momentum which states that momentum is always changing from one object to other, it can't be destroyed or created.

The law of momentum states :

$\tt{ \bull \: m_1 u_1 + m_2 u_2 = m_1 v_1 + m_2 v_2}$

Where,

$\tt{m_1 = mass \: of \: first \: object}$

$\tt{m_2 = mass \: of \: second \: object}$

$\tt{u_1 \: = \: initial \: velocity \: of \: first \: object}$

$\tt{u_2 = initial \: velocity \: of \: other \: object}$

$\tt{v_1 = final \: velocity \:of \: first \: object}$

$\tt{v_2 = final \: velocity \: of \: second \: object}$

Solution :

We are given with,

• Mass of first and second object
• Initial velocity of first and second object
• Final velocity of first object.

Hence, we know all the variables except one, that is Final velocity of second object.

So, we will create an equation and solve it for the final velocity of the second object.

So, according to the law of conservation of momentum:

$\tt{ \: m_1 u_1 + m_2 u_2 = m_1 v_1 + m_2 v_2}$

$\tt{ \implies \: (1 \times 2) + (2 \times 4) = (1 \times 3) + (2 \times v_2) }$

$\tt{ \implies 2 + 8 = 3 + 2v_2}$

$\tt{ \implies 2v_2 = 10 - 3}$

$\tt{ \implies 2v_2 = 7}$

$\large \tt{ \implies v_2 = \frac{7}{2} }$

$\red{ \underline{ \boxed{ \tt{ \bigstar \: v_2 = 3.5}}}}$

Hence, Final velocity of second Object = 3.5 m/s

__________________________

Verification :

Now, we will verify if we have got the correct answer or not.

We will use the law of momentum to check.

M1U1+M2U2 = LHS .

M1V1+M2V2 = RHS

According to this law, LHS should be equal to RHS.

So, LHS

= (1×2)+(2×4) = 2+8

= 10

RHS

= (1×3) + (2×3.5)

= 3+7

= 10

Hence, LHS = RHS ,

Our Answer is correct.

Hence Verified!

Answer 2

Answer:

The elements in the same group has similar number of valence electrons. They have identical number of electrons in their outermost shell. e.g. All the alkali metals in Group 1 have 1 valence electron, so they all tend to react the same way with other substances.