200kg Astronaut, 2.0 m/s, 100.0 N rocket ?

In summary: I can't believe it was this simple. In summary, The solution to the given problem is to apply a 100N force for 4 seconds in order to stop the motion of the 200kg astronaut and equipment moving at a velocity of 2.00 m/s towards an orbiting spacecraft. This can be determined using the equations F=ma, W=mg, m=w/g, and a=F/m.
  • #1
[SOLVED] 200kg Astronaut, 2.0 m/s, 100.0 N rocket ?

A 200.0 kg astronaut and equipment move with a velocity of 2.00 m/s toward an orbiting spacecraft . How long will the astronaut need to fire a 100.0 N rocket backpack to stop the motion relative to the spacecraft ? Give your answer in s.

Homework Equations


F=ma
W=mg
m=w/g
a=F/m

The Attempt at a Solution


I know I am missing something so simple. I have spent too long trying to solve this problem and have given up.

F=(200kg)(2 m/s)=400 kg*m/s=
F=400N/s

I don't know what to do with the 100N for the rocket pack, I'm getting lost in all the different conversions.

Please Help
 
Last edited:
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  • #2
Why don't you start by applying 100N for one second, and see what the final speed is?

There is definitely a way to apply the equations, but understand it intuitively and it'll make more sense.

Also, in your "F=(200kg)(2 m/s)=400 kg*m/s^2", you have an extra 1/s on the right side.
 
  • #3
jacksonjw81 said:
F=(200kg)(2 m/s)=400 kg*m/s^2
Look again at the units. That should be [itex]200\,\text{kg} 2\,\text{m}/\text{s} = 400 \,\text{kg-m}/\text{s}[/itex]. The product of velocity and mass is momentum, not force. An alternative expression for kg-m/s is Newton-seconds. That 400 kg-m/sec is the same as 400 Newton-seconds, and this form should tell you exactly how long the rocket pack needs to be fired.
 
  • #4
D H said:
Look again at the units. That should be [itex]200\,\text{kg} 2\,\text{m}/\text{s} = 400 \,\text{kg-m}/\text{s}[/itex]. The product of velocity and mass is momentum, not force. An alternative expression for kg-m/s is Newton-seconds. That 400 kg-m/sec is the same as 400 Newton-seconds, and this form should tell you exactly how long the rocket pack needs to be fired.

So if the Astronaut has a Force of 400 Newton-seconds and he fires a 100 N rocket then the answer will be 4 s?

If that is the correct answer I'm going to be pissed that is the solution I came up with when I first began working this problem. But, thought that it was to easy and couldn't be right.
 
  • #5
Pretty much. For each 100N force applied for 1 second, the decrease in velocity is 0.5m/s.

In 4 seconds, -2.0 m/s decrease in velocity.

Enjoy.
 
Last edited:
  • #6
iloveflickr said:
Pretty much. For each 100N force applied for 1 second, the decrease in velocity is 0.5m/s.

In 4 seconds, -2.0 m/s decrease in acceleration.

Enjoy.

Thanks
 

1. What does the "200kg" in "200kg Astronaut" refer to?

The "200kg" refers to the mass of the astronaut, which is a measure of the amount of matter that makes up their body.

2. What does the "2.0 m/s" in "2.0 m/s, 100.0 N rocket" represent?

The "2.0 m/s" represents the speed at which the astronaut is moving, measured in meters per second.

3. How is the "100.0 N" in "2.0 m/s, 100.0 N rocket" related to the rocket?

The "100.0 N" represents the force exerted by the rocket on the astronaut, which is necessary to propel them forward at a speed of 2.0 m/s.

4. What is the significance of the units used in the description "200kg Astronaut, 2.0 m/s, 100.0 N rocket"?

The units used in this description are important because they provide precise measurements for the mass, speed, and force involved in the scenario, allowing for accurate calculations and predictions.

5. How does the mass of the astronaut affect their movement in this scenario?

The mass of the astronaut plays a significant role in their movement, as it determines the amount of force needed to accelerate and decelerate them. A heavier astronaut would require more force to achieve the same speed as a lighter astronaut.

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