SOLUTION: a parachutist falls vertically with an uniform speed of 10m/s . At the moment when he is 40m from the ground , he drops a penknife. (use a= -10m/s2)(squared) a) what is the speed

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Question 919968: a parachutist falls vertically with an uniform speed of 10m/s . At the moment when he is 40m from the ground , he drops a penknife. (use a= -10m/s2)(squared)
a) what is the speed with which the penknife strikes the ground??
b) how long does the penknife take to reach the ground??
c) what is the difference between the penknife and the parachutist reaching the ground??

Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
For the penknife,
h%28t%29=-5t%5E2-10t%2B40
v%28t%29=-10-10t
Find the time t, when h%28t%29=0
-5t%5E2-10t%2B40=0
t%5E2%2B2t-8=0
%28t%2B4%29%28t-2%29=0
One solution
t-2=0
t=2
a)v=-10-10%282%29=-10-20=-30m%2Fs(Negative is downwards)
b)t=2s
c)The parachutist falls at a constant velocity.
10t%5Bp%5D=40
t%5Bp%5D=4 s
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.
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D=t%5Bp%5D-t=4-2=2s