Explanation

Step 1.We choose a longest string ABCDEFGHIJ in which we have to find out velocity of point J `(v_c)`
Step 2. Mark all the point A, B ................
Step 3. Write equation
`v_A + v_B + v_C + v_D + v_E + v_F + v_G + v_H + v_I + v_J = 0`
`v_A = v_D = v_E = v_H = v_I = 0 `
(No movementof that point because attached to fixed objects)
`implies v_B + v_c + v_F + v_G + v_J = 0" "...(1)`
`v_B = v_C = 5 m//s" "` (increases the length)
`v_F = v_G = 2m//s`
`" "`(It also increases the length)
Let us assume C is moving upward with velocity `V_c` so `V_c` negative because it decreasing the length `implies 5 + 5 + 2 + 2 – V_c = 0`
`v_C = 14 m//"sec"`(upward)