Starting from 100 ft away, your friend skates toward you and then passes you. She skates at a constant speed of 20 ft/s. Her distance d from you in feet after t seconds is given by d=|100-20t|. At what times is she 80 ft from you?

Question

Starting from 100 ft​ away, your friend skates toward you and then passes you. She skates at a constant speed of 20 ​ft/s. Her distance d from you in feet after t seconds is given by d=|100-20t|. At what times is she 80 ft from​ you?

oobleck · Answer

|100-20t| = 80 100-20t = ±80 20t = 100±80 t = 5±4 t = 1 or 9

Starting from 100 ft​ away, your friend skates toward you and then passes you. She skates at a constant speed of 20 ​ft/s. Her distance d from you in feet after t seconds is given by d=|100-20t|. At what times is she 80 ft from​ you?

Starting from 100 ft away, your friend skates toward you and then passes you. She skates at a constant speed of 20 ft/s. Her distance d from you in feet after t seconds is given by d=|100-20t|. At what times is she 80 ft from you?