Newton's Third law problem Astronaut and Force

In summary, when an 81.0 kg astronaut is sitting at rest on the launch pad, the force he exerts on his chair is 794 N. However, when he is accelerating straight up at 18.0 m/s^2, the correct calculation should be Fnet = m*a = 81 kg * 18 m/s^2 = 1458 N. The error in the previous calculation was most likely due to ignoring the direction and sign of the forces involved.
  • #1
sweetheart901
3
0
The question states:

How much force does an 81.0 kg astronaut exert on his chair while sitting at rest on the launch pad?

the answer that I got was 794 N
using...
W=m*g and
Fnet=w+fchair=0

But I cannot seem to get the right answer for this second question:

How much force does the astronaut exert on his chair while accelerating straight up at 18.0 m/s^2?


I know that Fnet= w+ Fchair
and also Fnet= m*a
so 81 kg * 18m/s^2= 794 + Fchair
the answer I get for Fchair is 664 but its not the correct answer.
what am I doing wrong??
 
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  • #2
Recall forces have directions associated with them, and thus signs. Be careful with your signs.
 
  • #3
Thank you! I guess that was my fault for making a silly error >.<
 

Related to Newton's Third law problem Astronaut and Force

1. What is Newton's Third Law of Motion?

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object will exert an equal force in the opposite direction on the first object.

2. How does Newton's Third Law apply to an astronaut in space?

When an astronaut pushes against a spacecraft to move themselves in a certain direction, the spacecraft will also experience an equal and opposite force in the opposite direction. This is because the astronaut is exerting a force on the spacecraft, and by Newton's Third Law, the spacecraft will exert an equal force back on the astronaut.

3. Can an astronaut move in space without any external force?

No, according to Newton's Third Law, every action has an equal and opposite reaction. In order for an astronaut to move in space, they must exert a force against something else, such as a spacecraft or a tool.

4. How does Newton's Third Law explain the movement of a rocket?

When a rocket launches, the burning fuel and gas are expelled from the back of the rocket at a high speed. According to Newton's Third Law, for every action (the expulsion of gas), there is an equal and opposite reaction (the rocket moves forward). This is known as Newton's Third Law of Motion in action.

5. What happens when two objects with different masses experience an equal and opposite force?

According to Newton's Third Law, the force will be equal but the acceleration will be different. The object with the smaller mass will experience a greater acceleration, while the object with the larger mass will experience a smaller acceleration. This is because acceleration is inversely proportional to mass, as described by Newton's Second Law of Motion.

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