A small steel ball is dropped into a long cylinder containing glycerine. Which one of the following is the correct representation of the velocity time graph for the transit of the ball?
(A)(see graph)
(B)(see graph)✓ Correct
(C)(see graph)
(D)(see graph)
Answer: (B)
Solution
As the steel ball falls through glycerine, the net downward force is
mg−FB−6πηrv=mdtdv
where FB is buoyancy and the last term is the viscous (Stokes) drag. Solving this linear equation gives
v(t)=K2K1(1−e−K2t)
for positive constants K1,K2. The velocity rises from zero and asymptotically approaches a constant terminal velocity, with continuously decreasing slope and no overshoot — the curve showing this saturating rise is option (2).
JEE Main · 2024 · 31 Jan 2024 · Shift 1 · Single correct option