One of my students recently attempted the following question: “At time $t=0$ particle is projected upwards with a speed of 10.5m/s from a point 10m above the ground. It hits the ground with a speed of 17.5m/s at time $T$. Find $T$.” They used the equation $s = vt – \frac 12 at^2$ and found $T = \frac{5}{7}$ and $T=\frac{20}{7}$…