# Homework Help: Calculating deacceleration force

1. Jun 3, 2009

### Valarg

1. The problem statement, all variables and given/known data

An object is moving at a velocity of 28m/s
The mass is 100kg
It deaccelerates from 28m/s to 0 in a distance of 5m

How much force (N) is needed to stop the object?

2. Relevant equations

3. The attempt at a solution

2. Jun 3, 2009

### PhanthomJay

You can use one of the kinematic eqations of motion to solve for the deceleration; and then use one of Newton's law to solve for the force. Or use energy methods. Please show what you have tried or your attempt at a solution.

3. Jun 3, 2009

### Valarg

Currently I got a 39,4C fever and have problems concentrating.

I understand that I probably need to use the f=ma basic formula but what I cant get my head around is the conversion to time.

Meaning I have the velocity, mass, deacceleration distance, and changes in velocity, still, I cant get my sore head to comprehend how to extract time from it, I´m stuck so unfortunatley I have no formula or attempt to a solution.

4. Jun 3, 2009

### PhanthomJay

Yow, you can't do too much with a 103 (degrees F) temp! Get well soon!

You don't need time; there is a basic kinematic equation that relates velocity with acceleration and distance. For a final velocity of 0, does v^2 = 2(a)(s) sound familiar, where v = 28, and s =5, then solve for a. Take care.

5. Jun 3, 2009

### Valarg

You are right, I really should leave this for tomorrow instead!

Thanx a bunch for your help! looks like it solved my problem! :)

6. Jun 3, 2009

### PhanthomJay

I might have given you a bit too much help, but while still working with a 39,4, you deserved it.