1. ## Question regarding physics?

I have these two problems that I cannot figure out...Can anyone show me what I need to do to complete it or how I should approach it? Any help would be appreciated!

A car traveling at 90 km/h strikes a tree. The front of the card compresses and the driver comes to rest after traveling .80 m. What was the average acceleration of the driver during the collision? Express the answer in terms of "g's" where 1 g = 9.8 m/s^2.

Show that the equation for the stopping distance of a car is d = vt - v^2/(2a), where v is the initial speed of the car, t is the drivers reaction time and a is the constant acceleration (and is negative).

2. Originally Posted by colerelm1
I have these two problems that I cannot figure out...Can anyone show me what I need to do to complete it or how I should approach it? Any help would be appreciated!

A car traveling at 90 km/h strikes a tree. The front of the card compresses and the driver comes to rest after traveling .80 m. What was the average acceleration of the driver during the collision? Express the answer in terms of "g's" where 1 g = 9.8 m/s^2.

Show that the equation for the stopping distance of a car is d = vt - v^2/(2a), where v is the initial speed of the car, t is the drivers reaction time and a is the constant acceleration (and is negative).

use the equation $v_f^2 = v_0^2 + 2ad$ . solve for $a$, then sub in your known values. you'll need to convert 90 km/hr to m/s.
during the reaction time, the car travels at a constant speed for the reaction time $t$ , distance traveled during the reaction time is $d = v_0 t$
to calculate the distance during braking, use the equation $v_f^2 = v_0^2 + 2ad$ , solve for $d$.