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

• jacksonjw81
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.

#### jacksonjw81

[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.

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.

Last edited:
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.

jacksonjw81 said:
F=(200kg)(2 m/s)=400 kg*m/s^2
Look again at the units. That should be $200\,\text{kg} 2\,\text{m}/\text{s} = 400 \,\text{kg-m}/\text{s}$. 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.

D H said:
Look again at the units. That should be $200\,\text{kg} 2\,\text{m}/\text{s} = 400 \,\text{kg-m}/\text{s}$. 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.

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:
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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