Posted by **Alex** on Tuesday, February 12, 2008 at 9:15pm.

1) A car traveling at 22m/s decelerates at a constant 1.5m/s^2. Calculate the time it takes to stop.

I first calculated the distance which is 160 m. Then I used the formula d=vit+1/2at^2. I got a quadratic -0.75t^2+22t-160. I got 13 or 16 as my time, but the answer says 15. Would it be correct to take the average of those times?

2) A stone is dropped from the roof of a high building. A second stone is dropped 1s later. How far apart are the stones when the second one has reached a speed of 23.0m/s?

I set this problem up by writing the given for stone 1 and stone 2.

Some equations I got were d(s1)= 4.905t^2 and ts2=ts1+1

I don't know how to do the problem.

- Physics -
**bobpursley**, Tuesday, February 12, 2008 at 10:01pm
1. No, not the average.

vf=vi+at

0=22-1.5t

t=15seconds.

Your method rounded distance to 160m. If you had not rounded, you would have gotten 15 seconds....

2.find the time of the first to get to that speed.

vf=gt solve for t, adn the distance fell.

Now, subtract one from that t, and find out how far the second fell.

Subtract the distances.

## Answer this Question

## Related Questions

- Calculus, AntiDerivatives - I need help with this problem: A car traveling at 43...
- physic - A car traveling at 80km/hr decelerates at 1.5m/s^2. Calculate a) the ...
- Physics - A race car can be slowed with a constant acceleration of -11 m/s^2 a. ...
- calc - a) A car is traveling at 50 mi/h when the brakes are fully applied, ...
- PLEASE HELP ME WITH PHYSICS!! - A truck is traveling at 16 m/s to the north. The...
- science - am confused. dont know what formula to use for this problem. A car ...
- Physics - A stone that starts at rest is in free fall for 8.0 s. a.Calculate the...
- physics - a car traveling at 43m/s decelerates at a rate of 7.1 m/s squared. how...
- Physics - An automobile is traveling 65mph. Its brakes decelerates at 6.0mps. ...
- Calculus - A car traveling at 72 mph starts braking and decelerates at a ...