Height of the image of my friend on the film

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The discussion revolves around verifying the calculations related to the height of an image in a film. The original poster doubts their answer, specifically questioning the conversion of a 29 m distance into centimeters and subsequently into millimeters. Participants emphasize the importance of accurate conversions and suggest re-evaluating the calculation of the image distance (d_i). It's noted that a crucial step may have been overlooked in the calculations. Accurate conversions and careful checking of all steps are essential for obtaining the correct height of the image.
syllll_213
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Homework Statement
You have a movie camera with a single lens of focal length 98 mm. You would like to take a picture of a friend who is standing 29 m away. Your friend is 155 cm tall, what is the height of the image of your friend on the film in mm?
Relevant Equations
1/f+1/di+1/do
1744710442452.png

Hi, I just want to check if my working is correct cuz I seems to get the wrong answer in my first attempt by inserting 0.054mm as the heigh.... the height seems a bit small to me.
 
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Check again your conversion of the 29 m distance into cm.
And make sure you get the distance image in the last step.
 
nasu said:
Check again your conversion of the 29 m distance into cm.
All conversions were to mm.
syllll_213 said:
View attachment 359892
Check your calculation of ##d_i##. There is something you forgot to do.
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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