Question

A ping-pong ball, having a diameter of 3.6 cm and weighing 2.4 g is served with a horizontal velocity of 10 m/sec and a spin that gives rise to a coefficient of lift of 0.2. Assuming the density of air to be 0.00129 gf/cc, the lift experienced by the ball is nearly

• A. 13gf
• B. 1.3gf
• C. 0.13 gf
• D. 0.013 gf

Answer 1

The correct option is B 1.3gf

$liftforce,F_L=C_L{A}_P\frac{\rho V^2}{2}$

$=0.2\times \frac{\pi \times (3.6{)}^2}{4}\times \frac{0.00129\times (1000{)}^2}{2}$

= 1.3 gf