1. A baseball is thrown vertically into the air with a speed of 24.0m/s. How long does it take to return to the ground? I found out the height that it could reach was 29m, then I used the formula d=vit+at^2/2. ---> 29=24t+9.81t^2/2. But I got two answers. THey are both positive. Why? Is anything wrong? 2. A car traveling 90km/h decelerates at a constant 1.6m/s^2. Find out the distance it travels during the first and third seconds. Here it means the distance when the time interval is from the first to the third second, which is 2 seconds? OR it asks you the instantaneous velocity which is at exactly the first second, and exactly the third second. btw, what do symbols like 'd0', 'a0' mean? they mean the distance and accelerations are 0? My teacher wrote these symbols. Maybe it's not formal. Thanks.