Problem 7.38

จาก\(\vec{s}=\vec{u}t+\frac{1}{2}\vec{a}t^{2}\)

îĵîĵĵ

\(rcosφ-rsinφ=(ucos\theta +usin\theta )t+\frac{1}{2}(-g)t^{2}\)

îĵîĵ

\(rcosφ - rsinφ = utcos\theta + (utsin\theta -\frac{gt^{2}}{2})\)

\(\therefore rsinφ =\frac{gt^{2}}{2} - utsinθ\) และ \(rcosφ = utcosθ\)

จะได้ \(\frac{rsinφ}{rcosφ}=\frac{gt^{2}}{2utcos\theta}-\frac{\sin \theta}{\cos \theta}\)

\(t =\frac{2u(\tan φ + \tan \theta )}{g}\)

จาก \(rcosφ = ut\)

\(r =\frac{2u^{2}(\tan φ + \tan \theta )}{gcosφ}\;\blacksquare\)