Solving Calc-Based Physics Problems: Object Position and Velocity at t=2s

[possum30540]

Homework Statement

An objects position as a function of time is given by r=12ti+(15t-5.0t^2)jm, where t is time in seconds. A: what is the onject's position at t=2 s. B what is its average velocity in the interval from t=o to t=2.0s.C: what is its instantaneous velocity at t=2?

Homework Equations

Derivative:12i+(15-10t)

V=change in r/change t

The Attempt at a Solution

A: simply plug 2 in for t in the original equation
B:take the derivative of the problem and plug in 2 for t
C: Dont really know . . .

 

[Doc Al]

A: simply plug 2 in for t in the original equation

OK.

B:take the derivative of the problem and plug in 2 for t

No derivatives needed, since you want the average velocity. (Use the formula you quoted.)

C: Dont really know . . .

Here's where you need a derivative.