# Jogger Vs. The Oak Tree

1. Jul 10, 2005

### StotleD

If a healthy but somewhat direction impaired individual (mass = 81.9 kg) is jogging through the woods and runs straight into a large oak tree at 4.7 m/s. Rebound speed is measured at 4.2 m/s in the opposite direction. If the time of contact with the tree is 46 milliseconds, what is the magnitude of the force that the tree exerts on the jogger?

2. Jul 10, 2005

### Pyrrhus

What have you done? I suggest applying the acceleration definition ($a = \frac{\Delta v}{\Delta t}$) directly into Newton's 2nd Law.

3. Jul 10, 2005

### KingNothing

This is a simple application of an impulse. I = Force * time, and is also the change in momentum. Momentum is mass times velocity. Momentum before = 81.9 * 4.7 = 384.93. Momentum after=81.9*-4.2= -343.98. Impulse = 728.91 = force * time. Time=.46. 728.91=force * .46. Force is then equal to 1584.59 newtons.