In a way...

For b)

Time taken = 8.86e13 / 3e8 = (8.86 / 3) x e(13-8)

OK

I finally was able to figure it out and it is 88600000000000 X 300000000=295333

Yes, that's correct, though you put the multiply sign in your post instead of the '/' sign ;)

Well done! :)

Why thank you! It was incredibly obvious and so I don'y know why I didn't get it.

If you don'y mind I got more hw and there are these 2 problems that I have not gotten.. do you mind helping me again please? =]

A student drops an object out the window of the top floor of a
High-rise dormitory.
(a) Neglecting air resistance, how fast is the object traveling when it
Strikes the ground at the end of 4.6 s?
(b) Express the answer to part a in miles per hour.
(c) How far, in meters, does the object fall in 4.6 s?

Now I know "a" is 45.09

But everything else is like.. Huh?

Then there is this problem..


Change in speed over change in time is acceleration...
A car travels on a straight, level road. Starting from rest, the car is
Going 30 m/s at the end of 3.0 sec.
(a) What is the acceleration of the car during the first 3.0
Seconds of motion?
In 9.0 more seconds, the car is going 40 m/s.
(b) What is the car's acceleration for this period
(during the 9 seconds)
The car then slows to 18 m/s in 2.0 seconds.
(c) What is the acceleration of the car during this period
Of time?
(d) What is the overall average acceleration of the car for the
Total time?

(a) Ok, using v = u + at,

v = 0 + 9.8(4.6) = 45.08 m/s

Seemed you made a typo... if you took a = 9.81, you'd get v = 9.81(4.6) = 45.126 m/s

(b) 1 mile = 1 609 metres
45.08 m = (1/1609) x 45.08 = 0.0280 miles

1 h = 3600 s

So, 45.08 m/s = 0.0280 mil/s

In 1 second, it does 0.0280 miles
In 3600 seconds, it does about (0.028 x 3600) = 101 miles.

Hence, speed = 101 miles/hr

(c) Use the formula:



u is the initial speed which is 0
t is the time which is 4.6 s
a is the acceleration due to gravity which is 9.8 m/s^2
s is the displacement, in this case, also the distance.
~~~~~~~~~~

Use the definition that you just gave me.

(a)

Final speed is 30 m/s.
Initial speed is zero since the car starts from rest.
Final time is 3 s.
Initial time is zero.

(b) Use again the same thing:


Final speed is 40 m/s.
Initial speed is 30 m/s.
Final time is 12 s. (in all, 9 + 3 = 12 seconds)
Initial time is 3 s. (during the 9 seconds means it starts at 3 seconds)

(c) Use the same thing as above and try to calculate the new times.

(d) It's the same thing. Just take the final and initial speeds at the last instant and when the time was started.

Post what you get! :)

So for C I got -11

Right, the acceleration of the car is indeed -11 m/s^2 :)