Question

Two skaters A and B of mass 50 kg and 70 kg respectively stand facing each other 6 metres apart. They then pull on a light rope stretched between them. How far has each moved when they meet?

• A. Both have moved 3 metres
• B. A moves 2.5 metres and B moves 3.5 metres.
• C. A moves 3.5 metres and B moves 2.5 metres.
• D. A moves 2 metres and B moves 4 metres.

Answer 1

The correct option is C A moves 3.5 metres and B moves 2.5 metres.

Here no any external force is applied taking two stakers A and B as a system.

then center of mass of both stakers will not change therefore they meat at center of mass, taking axis as shown in figure 1.

$X_{com}=\frac{50\times 0+70\times 6}{50+70}=\frac{70\times 6}{120}=3.5m$ from 50kg sketers.

$X_{com}$ = X-coordinate of center of mass.

So A mover 3.5cm

B mover (6 - 3.5) = 2.5m

Option C-correct