A particle P is projected vertically upwards from a point 20m above the ground with velocity 18m/s, no external forces act on it other than gravity. What will its speed be right before it hits the ground? Give your answer to one decimal place.

To start off we should list what we have and what we want to find. The initial velocity u= 18 m/s (taking upwards to be the positive direction). Acceleration a= - 9.8 m/s² (negative since gravity acts downwards). We want to find the speed of the particle right before it hits the ground so displacement s= - 20 m. Using the equation v² = u² + 2as we have v² =18² + 2*(-9.8)*(-20) = 716. Hence speed of particle before hitting the ground, v = 26.8 m/s, to 1d.p.