Register to reply

A problem involving Force in terms of time?

by kalpeshk2011
Tags: force, newton's laws, physics, velocity
Share this thread:
Mar2-12, 09:41 AM
P: 6
1. The problem statement, all variables and given/known data
There is a body of 3 kg which is moving to the right with a velocity of 10 m/s. A force of 6 N/s2t2 is applied on the body to the left. How much distane will the body have travelled from t=0 when its velocity is 0 m/s?

2. Relevant equations
I think they should be F=ma , dv/dt = a, ds/dt = v

3. The attempt at a solution
So by newton's second law,
so i got a = 2t2
Integrating this, i got v=t3+C and s=t4/4
Now i thought initial velocity will be -10m/s which i put in C
and V=0
so, 0 = t3-10 or t=2.31 seconds
I have no clue what to do after this. I thought i'll substitute the value of t in the equation with s in it, but some how i don't think its correct. And i don't have any answers to check my solution. please help..
Phys.Org News Partner Science news on
Experts defend operational earthquake forecasting, counter critiques
EU urged to convert TV frequencies to mobile broadband
Sierra Nevada freshwater runoff could drop 26 percent by 2100
Mar2-12, 10:04 AM
P: 1,195

Equation for s has to be written in a different form. With constant acceleration it is

s = V0t+.5at^2

You do not have constant acceleration.
Mar2-12, 10:06 AM
P: 6
is the equation s=t4/4 + C??

Mar2-12, 10:31 AM
P: 1,195
A problem involving Force in terms of time?

How about something like this

s = V0 * t + integral(a(t) * t)*dt

where a(t) is the acceleration, F(t)/m.

You have a mistake below for your time

"Integrating this, i got v=t^3"
Mar2-12, 10:34 AM
P: 1,195
Your equation s=t^4/4 is incorrect because your previous integration was incorrect.
Mar2-12, 10:36 AM
P: 6
But all this mathematics and integration in physics often confuses me. I don't know when to use which technique of integration. Moreover, I have only done the rudiments of calculus. Is there any definite way to know when to use which technique?
Mar2-12, 10:39 AM
P: 1,195
You can use whichever you feel the most comfortable. If you had solved for the time you could use definite integrals and avoid constants of integration.

When you integrate x^n you get (x^(n+1))/(n+1). Does this help?
Mar2-12, 10:53 AM
P: 1,195
And when you integrate

a*x^n you get a*(x^(n+1))/(n+1) where a is a constant. Do you see your mistake now?

Register to reply

Related Discussions
Force of gravity in terms of time, rather than distance. General Physics 3
Time problem involving Mass and a Pulley? Introductory Physics Homework 1
HELP! problem involving force of friction and normal force Introductory Physics Homework 7
Need help with a Force problem involving friction. Introductory Physics Homework 1
SHM problem involving an applied force Introductory Physics Homework 6