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Question Number 108175 by bemath last updated on 15/Aug/20

Commented by bemath last updated on 15/Aug/20

a man 6 feet tall walks at a rate 6 feet   per second away from a light that   is 15 feet above the ground.  When he is 10 feet from the base of the light  at what rate is the tip of his shadow  moving?

aman6feettallwalksatarate6feetpersecondawayfromalightthatis15feetabovetheground.Whenheis10feetfromthebaseofthelightatwhatrateisthetipofhisshadowmoving?

Commented by john santu last updated on 15/Aug/20

Commented by john santu last updated on 15/Aug/20

  (s_1 /(s_1 +s_2 )) = (6/(15)) ⇒(s_1 /(10+s_1 ))=(2/5)  5s_1 = 20+ 2s_1 ⇒s_1 = ((20)/3) feet  v = ((s_1 +s_2 )/t) = ((10+((20)/3))/(((5/3))))=((50)/5)=10 feet/second

s1s1+s2=615s110+s1=255s1=20+2s1s1=203feetv=s1+s2t=10+203(53)=505=10feet/second

Answered by mr W last updated on 15/Aug/20

x=position of the man  s=posistion of the tip of the shadow  l=length of the shadow  ((s−x)/6)=(s/(15))  ⇒s=(5/3)x  l=s−x=(2/3)x  (ds/dt)=(5/3)×(dx/dt)=(5/3)×6=10 ft/sec  (dl/dt)=(2/3)×(dx/dt)=(2/3)×6=4 ft/sec

x=positionofthemans=posistionofthetipoftheshadowl=lengthoftheshadowsx6=s15s=53xl=sx=23xdsdt=53×dxdt=53×6=10ft/secdldt=23×dxdt=23×6=4ft/sec

Commented by bemath last updated on 15/Aug/20

thank you mr W

thankyoumrW

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