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Question Number 217148 by Marzuk last updated on 03/Mar/25

I have seen a relationship in the curve  path of a thrown object at β   while the total passed distance D_v  and  highest point had passedD_u   then β = arctan(((4D_u )/D_v ))  but cant find the proof.  I would like to say would anyone like  to proove it?then please.

IhaveseenarelationshipinthecurvepathofathrownobjectatβwhilethetotalpasseddistanceDvandhighestpointhadpassedDuthenβ=arctan(4DuDv)butcantfindtheproof.Iwouldliketosaywouldanyoneliketoprooveit?thenplease.

Answered by mr W last updated on 03/Mar/25

Commented by mr W last updated on 03/Mar/25

the track of a thrown object is a  parabola (red curce in diagram).  for a parabola there are the   geometrical relationships as shown.  tan β=((2D_v )/(0.5 D_u ))=((4D_v )/D_u )  ⇒β=arctan (((4D_v )/D_u ))  certainly we can also prove this  using the equations for projectile  motion, see below.

thetrackofathrownobjectisaparabola(redcurceindiagram).foraparabolatherearethegeometricalrelationshipsasshown.tanβ=2Dv0.5Du=4DvDuβ=arctan(4DvDu)certainlywecanalsoprovethisusingtheequationsforprojectilemotion,seebelow.

Answered by mr W last updated on 03/Mar/25

Commented by Marzuk last updated on 03/Mar/25

Much appreciated!It might need some  more expansion to publish it.I will  do it.  At the conclusion,thanks for the key  proof.

Muchappreciated!Itmightneedsomemoreexpansiontopublishit.Iwilldoit.Attheconclusion,thanksforthekeyproof.

Commented by mr W last updated on 03/Mar/25

x=(u cos β)t  y=(u sin β)t−((gt^2 )/2)  at y=y_(max) =D_v :  (dy/dt)=u sin β−gt=0 ⇒t=((u sin β)/g)=t_1   y∣_(t=t_1 ) =D_v =(u sin β)×(((u sin β)/g))−(g/2)(((u sin β)/g))^2   ⇒D_v =((u^2  sin^2  β)/(2g))   ...(i)  at y=0, i.e. point B:  (u sin θ)t−((gt^2 )/2)=0 ⇒t=t_2 =((2u sin β)/g)=2t_1   x∣_(t=t_2 ) =D_u =(u cos β)×(((2u sin β)/g))  ⇒D_u =((2u^2  sin β cos β)/g)   ...(ii)  (i)/(ii):  (D_v /D_u )=((sin β)/(4 cos β))=((tan β)/4)  ⇒β=arctan(((4D_v )/D_u ))

x=(ucosβ)ty=(usinβ)tgt22aty=ymax=Dv:dydt=usinβgt=0t=usinβg=t1yt=t1=Dv=(usinβ)×(usinβg)g2(usinβg)2Dv=u2sin2β2g...(i)aty=0,i.e.pointB:(usinθ)tgt22=0t=t2=2usinβg=2t1xt=t2=Du=(ucosβ)×(2usinβg)Du=2u2sinβcosβg...(ii)(i)/(ii):DvDu=sinβ4cosβ=tanβ4β=arctan(4DvDu)

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