Math Is Fun Forum

taylor_2009

Member

Registered: 2010-01-25

Posts: 28

When is the object traveling at 6 km/h?

An object moving in a straight line travels s(t) kilometers in t hours, where s(t)=7t²+t.
(a) What is the object's velocity when t=6?
(b) How far has the object traveled in 6 hours?
(c) When is the object traveling at a rate of 6 km/h?

For (a) I got: 85 km/h
For (b) I got: 258 km.

I can't figure out (c). Please help.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: When is the object traveling at 6 km/h?

Hi taylor_2009;

a and b are correct. For c)

s = 7t²+t.

v =ds / dt = 14 t + 1

6 = 14 t + 1

5 = 14 t

t = 5 / 14 s

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.