6. A car traveling at a speed of 30.0 m/s encounters an emergency and comes to a complete stop. How much time will it take for the car to stop if it decelerates at -4.0 m/s2? Given: speed = 30m/s final speed = 0m/s acceleration = -4.0m/s^2
Asking For: time?

7. After traveling for 6.0 seconds, a runner reaches a speed of 10 m/s. What is the runner’s acceleration?

Given:
Asking for

7.5s1.6666 repeating or 1.67 m/s²

Explanation:

the equation you have to use is Vfinal=Vstart+acceleration•time

(I'm gonna simplify to Vf=Vs+at)

so you gotta rework it for the two equationsfor the first equation you need time so take Vf=Vs+at and subtract Vs on both sides to get Vf–Vs=atthen divide acceleration on both sides to get t=(Vf–Vs)/afor the second problem equation need the equation a=(Vf–Vs)/t (just divide time on both sides instead of acceleration)so you the plug in

(I don't put the units in to the problem unless needed)

1. t=(Vf–Vs)/a to t=(0–30)/-4.0

t= -30/-4.0t=7.5 seconds

2. a=(Vf–Vs)/t to a=(10–0)/6.0

a= 10/6.0a= 1.67m/s²

(I'm assuming the that for number two they started at rest so it would be 0m/s for velocity start)