Most of the metals we use are alloy metals combined with other materials. Brass is an alloy made of copper and zinc. This table shows the parts of copper and zinc used to make a batch of brass.
Copper, in Zinc, in
pounds pounds

Astuntman jumping off a 20-m-high building is modeled by the equation h=20-5t^2, where t is the same in seconds. a high-speed camera is ready to film him between 15m and 10m above the ground. for which interval of time should the camera film him?