Word Problem

Question

The height, y meters, of an object projected directly upwards from the ground can be modeled by y=20t-5t², where t is the time in seconds after it leaves the ground. 

 

i. Find the height of the object 2 seconds after it leaves the ground.

ii. When will the object be 15m above the ground.

Answer 1

i.

 

Evaluate y when t=2

 

 

ii.

 

Set  y=15  and solve for t.

 

-5t² + 20t = 15

 

-5t² + 20t - 15 = 0

 

 

Solve the quadratic equation for t.