Question and Answers Forum

All Questions      Topic List

Others Questions

Previous in All Question      Next in All Question      

Previous in Others      Next in Others      

Question Number 20316 by Tinkutara last updated on 25/Aug/17

$$\mathrm{If}\mathrm{at}\mathrm{a}\mathrm{height}\mathrm{of}40\mathrm{m},\mathrm{the}\mathrm{direction}\mathrm{of}$$$$\mathrm{motion}\mathrm{of}\mathrm{a}\mathrm{projectile}\mathrm{makes}\mathrm{an}\mathrm{angle}$$$$\pi /4\mathrm{with}\mathrm{the}\mathrm{horizontal},\mathrm{then}\mathrm{its}\mathrm{initial}$$$$\mathrm{velocity}\mathrm{and}\mathrm{angle}\mathrm{of}\mathrm{projection}\mathrm{are},$$$$\mathrm{respectively}$$$$\left(a\right)30,\frac{1}{2}{\cos }^{-1}(-\frac{4}{5})$$$$\left(b\right)30,\frac{1}{2}{\cos }^{-1}(-\frac{1}{2})$$$$\left(c\right)50,\frac{1}{2}{\cos }^{-1}(-\frac{8}{25})$$$$\left(d\right)60,\frac{1}{2}{\cos }^{-1}(-\frac{1}{4})$$

Commented by Tinkutara last updated on 25/Aug/17

$$\mathrm{I}\mathrm{think}\mathrm{velocity}\mathrm{of}\mathrm{projection}\mathrm{should}\mathrm{be}$$$$\mathrm{given}.{\mathrm{Isn}}^{\prime }\mathrm{t}\mathrm{it}?$$

Commented by ajfour last updated on 25/Aug/17

$$onemoreinformationneedbe$$$$given..$$

Commented by Tinkutara last updated on 25/Aug/17

$$\mathrm{This}\mathrm{is}\mathrm{the}\mathrm{wrong}\mathrm{solution}\mathrm{given}\mathrm{in}$$$$\mathrm{book}\mathrm{or}\mathrm{it}\mathrm{is}\mathrm{correct}?$$

Commented by Tinkutara last updated on 25/Aug/17

Commented by Joel577 last updated on 25/Aug/17

$$howdiditsay50m/s?$$

Commented by Tinkutara last updated on 25/Aug/17

$$\mathrm{Yes},\mathrm{so}\mathrm{this}\mathrm{solution}\mathrm{is}\mathrm{wrong}\mathrm{but}\mathrm{it}\mathrm{is}$$$$\mathrm{in}\mathrm{my}\mathrm{book}.$$

Commented by ajfour last updated on 25/Aug/17

$$-1⩽\cos 2\theta ⩽1$$$$-1⩽-\frac{2gh}{u^2}⩽1$$$$\Rightarrow u^2⩾2gh$$$$u^2⩾800$$$$u⩾20\sqrt{2}(\approx 28m/s).$$$$ifu=30m/s\Rightarrow \theta =\frac{1}{2}{\cos }^{-1}(-\frac{8}{9})$$$$ifu=40m/s\Rightarrow \theta =\frac{1}{2}{\cos }^{-1}(-\frac{1}{2})$$$$ifu=50m/s\Rightarrow \theta =\frac{1}{2}{\cos }^{-1}(-\frac{8}{25})$$$$ifu=60m/s\Rightarrow \theta =\frac{1}{2}{\cos }^{-1}(-\frac{2}{9})$$$$\left(c\right)isoneofthepossiblesolutions$$$$\left(a\right),\left(b\right),\left(d\right)arejustnotpossible.$$

Commented by Tinkutara last updated on 25/Aug/17

$$\mathrm{Thanks}\mathrm{you}\mathrm{very}\mathrm{much}\mathrm{Sir}!\mathrm{So}\mathrm{it}\mathrm{is}\mathrm{to}$$$$\mathrm{be}\mathrm{seen}\mathrm{by}\mathrm{the}\mathrm{options}.$$

Terms of Service

Privacy Policy

Contact: info@tinkutara.com