Question

A collar of mass 10 kg is released from rest from position A, when spring is in natural length and slides along a rough vertical fixed rod. The block comes to rest at point B, 4 m below the point A. The spring constant of spring is 100 N/m and natural length of spring is 3 m. Find work done by friction (‘O’ is a fixed point)

• A. -100 J
  
• B. -200 J
  
• C. -300 J
  
• D. -400 J

Answer 1

The correct option is B

-200 J

The energy stored in the spring = $\frac{1}{2}k{x}_0^2=200J.$ Loss in energy due to gravity = mg(AB) = 400J.
Hence loss in energy due to friction = 200 – 400 = – 200 J