# Homework Help: Kathy Kool needs some help

1. Nov 11, 2008

### jp0108

1. The problem statement, all variables and given/known data
A young woman named Kathy Kool buys a
sports car that can accelerate at the rate of
4.56 m/s2. She decides to test the car by drag
racing with another speedster, Stan Speedy.
Both start from rest, but experienced Stan
leaves the starting line 0.51 s before Kathy.
Stan moves with a constant acceleration of
3.43 m/s2 and Kathy maintains an accelera-
tion of 4.56 m/s2.
Find the time it takes Kathy to overtake
Stan. Answer in units of s.

The formulas are:

vf = vi + at

d = vit + 1/2at^2

d = 1/2 (vi + vf) delta t

a = delta v/ t

v = d/t

KEY:
v: m/s
d: m
t: s
a: m/s^2
vi: initial velocity
vf: finial velocity
delta v: change in velocity

Last edited: Nov 11, 2008
2. Nov 11, 2008

### Staff: Mentor

You need to show us the relevant equations, and show us your attempt at a solution before we can help you. That's the PF Rules (see the link at the top of the page).

3. Nov 11, 2008

### jp0108

the formulas are:

vf = vi + at

d = vit + 1/2at^2

d = 1/2 (vi + vf) delta t

a = delta v/ t

v = d/t

KEy:
v: m/s
d: m
t: s
a: m/s^2
vi: initial velocity
vf: finial velocity
delta v: change in velocity

Last edited: Nov 11, 2008
4. Nov 11, 2008

### Staff: Mentor

This would be the most useful equation of the bunch for this problem. Why?

Now write the two equations for the d(t) of the two cars, including the initial conditions you've been given, and find at what time t the two d(t) numbers are equal...