Motion in a Plane
A projectile is launched with speed u at an angle theta to the horizontal. Derive expressions for its time of flight, maximum height and horizontal range.
Reveal model answer + marking pointsHide answer▾
Resolve u into ux = u cos(theta) and uy = u sin(theta). Vertical motion has acceleration -g. Time of flight: uy - g(T/2) = 0 at the top, so T = 2u sin(theta)/g. Maximum height: H = uy^2/2g = u^2 sin^2(theta)/2g. Horizontal range: R = ux * T = u cos(theta) * 2u sin(theta)/g = u^2 sin(2 theta)/g. R is maximum when theta = 45 degrees.
T = 2u sin(theta)/g ; H = u^2 sin^2(theta)/2g ; R = u^2 sin(2theta)/g
Marking-scheme points
- ✓Resolve into horizontal and vertical components
- ✓T = 2u sin(theta)/g
- ✓H = u^2 sin^2(theta)/2g
- ✓R = u^2 sin(2 theta)/g
- ✓R max at theta = 45 deg