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mychellbella
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Conservation of momentum problem and kinematics!?
Hi, I've been working on this problem for the last three hours, I hope someone can help. In fact, the solution I keep getting is double the correct answer (the answers are in the back of the book, but not the how).
An 80 kg astronaut is stranded 10 m from his spaceship in free space. In order to get back to his ship, he throws a 2.0 kg piece of equipment w/ a speed of 0.5 m/s directly away from the ship. How long will it take for him to reach the ship?
man object
m1=80kg m2= 2.0kg
vo1=0 vo2= 0
vf1= ? vf2= .5m/s
so, i started by treating this like a gun and bullet problem since he will be recoiling.
Pf(momentum final) = Po (momentum orignal) = 0
Pf=m1vf1+ m2vf2
0= m1vf1 +m2vf2
vf1= (-m2/m1)*vf2
vf1=(-2.0kg/80kg)*.5m/s
vf1= .0125 m/s
okay, now i find the acceleration, so i can then use a kinematic equation to find the time. I only use the info for the man and vo is .0125 m/s and vf=0. x=10m.
a=(vf^2-vo^2)/2x
a=(0-.0125m/s^2)/2(10m)
a=-7.81*10^-6 m/s^2
t=(vf-vo)/a
t=(0-.0125m/s)/-7.81*10^6 m/s^2
t =1600 seconds
The problem, is that the book is saying the anwer is 800 seconds. What am I doing wrong! Please help! thank you!
Hi, I've been working on this problem for the last three hours, I hope someone can help. In fact, the solution I keep getting is double the correct answer (the answers are in the back of the book, but not the how).
An 80 kg astronaut is stranded 10 m from his spaceship in free space. In order to get back to his ship, he throws a 2.0 kg piece of equipment w/ a speed of 0.5 m/s directly away from the ship. How long will it take for him to reach the ship?
man object
m1=80kg m2= 2.0kg
vo1=0 vo2= 0
vf1= ? vf2= .5m/s
so, i started by treating this like a gun and bullet problem since he will be recoiling.
Pf(momentum final) = Po (momentum orignal) = 0
Pf=m1vf1+ m2vf2
0= m1vf1 +m2vf2
vf1= (-m2/m1)*vf2
vf1=(-2.0kg/80kg)*.5m/s
vf1= .0125 m/s
okay, now i find the acceleration, so i can then use a kinematic equation to find the time. I only use the info for the man and vo is .0125 m/s and vf=0. x=10m.
a=(vf^2-vo^2)/2x
a=(0-.0125m/s^2)/2(10m)
a=-7.81*10^-6 m/s^2
t=(vf-vo)/a
t=(0-.0125m/s)/-7.81*10^6 m/s^2
t =1600 seconds
The problem, is that the book is saying the anwer is 800 seconds. What am I doing wrong! Please help! thank you!