Need to find the net force and the average force .

In summary: B on A.In summary, we need to find the net force and average force acting on a bullet that strikes a stationary block of wood at a speed of 400m/s and penetrates to a depth of 3.0cm. Using the equations Fnet= m x a and W=1/2mv^2, the net force is found to be 79.998 N. To calculate the average force, the equation 2ax = (vf)^2 - (vi)^2 is used and the result is 32000 N. Using momentum is not applicable since the block is fixed, and heat generated from the impact can be calculated by finding the kinetic energy lost when the
  • #1
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Need to find the net force and the average force...

1. Homework Statement

A bullet of mass 12 g strikes a stationary fixed block of wood at a speed of 400m/s, penetrating to a depth of 3.0cm. Calculate the average net force acting on the bullet while it is in the wood. Calculate the average force exerted on the wood by the bullet.

2. Homework Equations
Fnet= m x a
W=1/2mv^2

3. The Attempt at a Solution
I found the force net using the kinetic energy and work equation. I don't really know how to find the average force.
 
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  • #2


wow, someone please help I have a bunch of similar question and I need help!
 
  • #3


Try using this equation: 2ax = (vf)^2 - (vi)^2.
Find the acceleration.
Use Newton's second law to calculate force.
This is the only possible solution I can see.

Note: use above equation only if a is constant.
I like your approach using work-kinetic energy theorem.
One point: the force exerted on the wood by the bullet isn't the same force exerted by the wood on the bullet with opposite direction? (3rd Newton's Law)
 
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  • #4


So would the acceleration be 6666.5m/s^2
 
  • #5


That would be possible only if the acceleration is constant. I suppose it isn't, so the work-kinetic energy theorem seems to be the only option.
 
  • #6


Fnet is equal to 79.998 N. for part b it wants me to find force average. when i think of force average I think of momentum. but i don't have enough information to find force average using momentum. Do you know any other equations?
 
  • #7


Woah what. :S Ok you said to use the 2ax = (vf)^2 - (vi)^2. and I got 6666.5 m/s^2. is it wrong? does that mean I have to go back to my original idea? Now I am beyond confused.
 
  • #8


Mmmm... I have just tried to solve this problem using the equation of kinematics I gave and the work-kinetic energy theorem and both gave me that the average force is 32000 N. Do you know what is the correct answer (from the textbook, if you took the problem from one)?

About using momentum, you must have a function that describes how it changes over time, in order to derivate it and find force. Then, you will need to integrate the force and divide it by the time interval. Unfortunately, I see no way of doing this for this kind of exercise.
 
  • #9


Momentum wouldn't apply because the block is fixed. It seems like it's just an equal opposite thing. There is of course heat generated but I don't see how that could be calculated from the info given.
 
  • #10


The heat would be all the kinetic energy lost (neglecting sound) when the bullet comes to rest.
 
  • #11


You have mechanical work done in ripping the wood I would think as well as heat but I don't see how it would change the answer.
 
  • #12


also the bullet may be flattened. but regardless, you only start with a certain amount of energy available and force ab is - Fba
 
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What is net force and average force?

Net force is the overall force acting on an object, taking into account both magnitude and direction. Average force is the total force acting on an object over a certain period of time.

How do you calculate net force and average force?

To calculate net force, you must add all the forces acting on an object together, taking into account their direction. Average force can be calculated by dividing the total force by the time period over which it is applied.

Why is it important to find net force and average force?

Understanding net force and average force is crucial for analyzing the motion of objects and predicting their behavior. It allows us to determine the acceleration and velocity of an object, and to make predictions about its future motion.

What factors affect the net force and average force?

The net force on an object is affected by the magnitude and direction of all the individual forces acting on it. Average force is influenced by the duration of the forces and any changes in magnitude or direction over time.

Can net force and average force be negative?

Yes, net force and average force can be negative if the forces acting on an object are in opposite directions or if there is a decrease in magnitude over time. A negative force indicates that the object is experiencing a deceleration or a change in direction.

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