Finding Net Force in Physics Homework

AI Thread Summary
To find the net force experienced by Person A, first determine the acceleration using the kinematic equation d = (vi)(t) + (1/2)(a)(t)^2, where the displacement (d) is 40 m, initial velocity (vi) is 4 m/s, and time (t) is 5 seconds. Solving the equation yields an acceleration of 1.6 m/s². Next, apply Newton's second law, F = ma, using Person A's mass of 40 kg and the calculated acceleration. The resulting net force is 64 N [E]. This process illustrates how to connect kinematic equations with Newton's laws to solve physics problems.
dois
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Homework Statement



the questions says,
"Person A who's mass is 40kg, is being pulled across the ground by a horse at a speed of 4 m/s [E]. All of a sudden the horse accelerates for a period of 5 seconds. During this time person A experiences a displacement of 40 m [E]. What net force was experienced by person A?"

Homework Equations


The Attempt at a Solution



I have no idea how to even begin this question. I'm not sure what equations i even need to use.
 
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Hi dois, welcome to PF.
In the problem the initial velocity, duration pof acceleration and the displacement is given. Can find find a kinematic equation from the textbook which relates these quantities with acceleration?
 
dois said:

Homework Statement



the questions says,
"Person A who's mass is 40kg, is being pulled across the ground by a horse at a speed of 4 m/s [E]. All of a sudden the horse accelerates for a period of 5 seconds. During this time person A experiences a displacement of 40 m [E]. What net force was experienced by person A?"


Here is a little more help. This can be approached as a two step question. Recall that Newton's second law says F = ma. You have the mass of the person so you need the acceleration. You can find the acceleration from the information given in the problem using a kinematics equation that relates distance, velocity, time, and acceleration.
 
ok so first I would need to find the acceleration so I can sub that answer into F= m*a
so i would use
acceleration= v/t
?
 
dois said:
ok so first I would need to find the acceleration so I can sub that answer into F= m*a
so i would use
acceleration= v/t
?

The problem gives you the initial speed (Vi), time (t), and displacement (d). If you take a look at the kinematic equations, you'll find that you can solve one of them for acceleration. The kinematic equation you're looking for is this one.

d = (vi)(t) + (1/2)(a)(t)^2

Go from there.
 
Ok so if we sub all of our know variables into the equation
d = (vi)(t) + (1/2)(a)(t)^2
then we would get:
40= 4x5 +1/2 (?) x5^2
40=20 +25/2 x
20=25/2 x
20=12 1/2 x
x= 1.6

but as soon as i figure out the acceleration where do I go from there to find out the net force?
 
Last edited:
dois said:
Ok so if we sub all of our know variables into the equation
d = (vi)(t) + (1/2)(a)(t)^2
then we would get:
40= 4x5 +1/2 (?) x5^2
40=20 +25/2 x
20=25/2 x
20=12 1/2 x
x= 1.6

but as soon as i figure out the acceleration where do I go from there to find out the net force?

Okay, your algebra looks good, so a = 1.6 m/sec squared.

Remember I said this was a two step question. Go back and read my first post. That indicates what you do next.
 
So then we would sub a into F=ma
so (40kg) (1.6 m/s)
and then our answer would be Fnet= 64 kg m/s [E]
 
That should do it, except that the units you give are wrong. The seconds should be squared. That combination of units has its own name: Newtons.
 
  • #10
alright, thank you!
 
  • #11
You are quite welcome.
 
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