Question

A ball of mass 2 kg is projected up in the air from ground level with a speed 20 ms-1. it experiences constant air resistance R. It returns ground level with a speed of 15 ms-1 find R

Answer 1

$$a_1=\frac{R}{m}+g$$

$$v_1^2-0^2=2a_1h$$

$$a_2=g-\frac{R}{m}$$

$$v_2^2-0^2=2a_2h$$

Thus,

$$\frac{a_1}{a_2}=\frac{\frac{R}{m}+g}{g-\frac{R}{m}}=\frac{v_1^2}{v_2^2}$$

$$\frac{\frac{R}{2}+9.8}{9.8-\frac{R}{2}}=\frac{20^2}{15^2}$$

$$R=5.5\ N$$