1. Given data

• Speed of each car: $u = 20\,\text{m s}^{-1}$
• Retardation of each car: $a = -2\,\text{m s}^{-2}$
• Initial distance between cars: $300\,\text{m}$

2. Find stopping distance of one car

Using the equation:

$v^2 = u^2 + 2as$

Since the car comes to rest, $v=0$.

So,

$0 = (20)^2 + 2(-2)s$

$0 = 400 - 4s$

$4s = 400$

$s = 100\,\text{m}$

Thus, each car travels $100\,\text{m}$ before stopping.

3. Total distance covered by both cars before coming to rest

$100 + 100 = 200\,\text{m}$

4. Distance left between them

Initial separation was $300\,\text{m}$, so remaining distance is:

$300 - 200 = 100\,\text{m}$

5. Check options

• A: $25\,\text{m}$ ❌
• B: $100\,\text{m}$ ✅
• C: $50\,\text{m}$ ❌
• D: $200\,\text{m}$ ❌

Therefore, the correct answer is B.