physics q (1 Viewer)

astroman · May 22, 2016

A 74 kg fireman is sliding down a firepole. How much frictional force must he use in order to arrive from the first floor to the ground floor (a distance of 3 m) in exactly 2.7 seconds?

jathu123 · May 22, 2016

$\noindent $assuming the fireman starts from rest at the 1st floor, the required acceleration can be calculated using the formula $ s=ut+\frac{1}{2}at^{2}. \\ -3=0+\frac{1}{2}a(2.7)^{2} \\ a =-0.823045... ms^{-2} \\ \therefore $ required force $ = ma = 74\times -0.823 = -60.905 $N$ \\ $But the force due to gravity is $ 74\times -9.8 = -725.2$ N$ \\ \therefore $ Force due to friction, F$_f, =725.2-90.905 = 664.3 $ N$$

However, I'm not sure if it's 100% right, so its best if you wait for Integrand's or someone else's response

porcupinetree · May 22, 2016

jathu123 said:
$\noindent $assuming the fireman starts from rest at the 1st floor, the required acceleration can be calculated using the formula $ s=ut+\frac{1}{2}at^{2}. \\ -3=0+\frac{1}{2}a(2.7)^{2} \\ a =-0.823045... ms^{-2} \\ \therefore $ required force $ = ma = 74\times -0.823 = -60.905 $N$ \\ $But the force due to gravity is $ 74\times -9.8 = -725.2$ N$ \\ \therefore $ Force due to friction, F$_f, =725.2-90.905 = 664.3 $ N$$

However, I'm not sure if it's 100% right, so its best if you wait for Integrand's or someone else's response

Looks good to me.

astroman · May 23, 2016

brain fart,

At a location where g = 9.80 m/s2, an object is thrown vertically down with an initial speed of 30.0 m/s. After 3.00 s, the object will have traveled?

InteGrand · May 23, 2016

astroman said:
brain fart,

At a location where g = 9.80 m/s2, an object is thrown vertically down with an initial speed of 30.0 m/s. After 3.00 s, the object will have traveled?

s = ut + ½ a t², with u = 30.0 m/s, t = 3 s, and a = 9.80 m/s².

astroman · May 23, 2016

InteGrand said:
s = ut + ½ a t², with u = 30.0 m/s, t = 3 s, and a = 9.80 m/s².

cheers

physics q (1 Viewer)

astroman

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jathu123

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porcupinetree

not actually a porcupine

astroman

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InteGrand

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astroman

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