# Newton's Laws of Motion

• alexdude777
In summary, the quarterback must throw the ball at a speed of 159.53 m/s in order to hit the 200 yd mark.

## Homework Statement

A 41-kg box is thrown at a speed of 235 m/s and is brought to a halt in a collision that lasts for a time of 6.8 ms. What is the magnitude of the average net force that acts on the box during the collision?

## Homework Equations

Sum of Forces = m*a

## The Attempt at a Solution

Well I tried t=6.8, v(o) = 235 m/s, v = 0, , and tried to solve for acceleration, which i got -34.56. but putting that in the sum of forces = m*a is not giving me the correct solution. i suck at physics :(

Hi alexdude777.
Is it the time 6.8 seconds or miliseconds ?

step one of solving physics problem is to draw a picture, so where's your drawing? and then show your work. plus you can never have a (-) acceleration the (-) sign is just to show the direction.

It's definitely 6.8 milliseconds

Well I did make a drawing but how would I post it here? I mean it was just a box that I labeled 41-kg, with a vector towards the wall labeling the direction and velocity(235m/s), and then hitting a wall. Then I had t=6.8ms on the side

I am terrible at the stuff...I am going to fail :(

welcome to pf!

hi alexdude777! welcome to pf!
alexdude777 said:
Well I tried t=6.8, v(o) = 235 m/s, v = 0, , and tried to solve for acceleration, which i got -34.56.

as Karlx points out, you won't get 34.56 if you use .0068

Then I get it to equal -34558.823 ... there is NO way that can be right right? I was using that v=v(o) + at for the equation... am i even close to on the right track or no?

Hi alexdude777.
Why do you think it cannot be right?

HOLY CRAP it was right! Wow. Thanks so much. I really appreciate it guys. Can I ask a projectile motion question here if I show you guys all the work I have tried?

Here is the question

A quarterback claims that he can throw the football a horizontal distance of 183 m (200 yd). Furthermore, he claims that he can do this by launching the ball at the relatively low angle of 35° above the horizontal. To evaluate his claim, determine the speed with which this quarterback must throw the ball.

Well I drew a picture. The line is x=183m, with theta being 35degrees. I need to find v(o)

a(x) = 0
t = ?
x = 183

v(oy) = ?
v(y) = ?
a(y) = -9.8m/s^2
t = ?
and I tried finding y with some trig...is it 159.53, the max height of the ball?

I guess I am just stuck here because I don't know where to go next, the book is not doing that great of a job explaining this or at least with a problem similar to this. I know I need to use the 35degrees and use trig. maybe to find the initial velocity in both the x and y direction? but i don't know what the length of the sides of the triangle would be, because the only other thing i have is how long x is. Any advice on how to get started?

You are on the rigth way, alexdude.
You must see the motion of the ball as a composition of two kinds of motion: one in the horinzontal axis and another in the vertical axis.
Which kind of motion on the x axis?
Which kind of motion on the y axis?
Try to write the equations of motion for each axis.
And from it, up to you...

## What are Newton's Laws of Motion?

Newton's Laws of Motion are three laws that describe the relationship between an object's motion and the forces acting upon it. They were developed by Sir Isaac Newton in the 17th century and are considered fundamental principles in the study of physics.

## What is the first law of motion?

The first law, also known as the law of inertia, states that an object at rest will remain at rest and an object in motion will continue in a straight line at a constant speed unless acted upon by an external force.

## What is the second law of motion?

The second law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. This can be expressed as the equation F=ma, where F is the net force, m is the mass, and a is the acceleration.

## What is the third law of motion?

The third law, also known as the law of action and reaction, 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 and opposite force back.

## How are Newton's Laws of Motion applied in real life?

Newton's Laws of Motion are essential in understanding and predicting the motion of objects in our everyday lives. They are used in fields such as engineering, sports, and transportation to design and improve systems and objects. For example, the first law explains why a seatbelt is necessary in a car and the second law is used to calculate the force needed to launch a rocket into space.