AP physics B problem help D:

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Q wrote on 2010-09-17 00:40

The problem is something on projectile motion btw.

A projectile is shot from the edge of a cliff 125m above the ground level with an initial speed of 65.0m/s at an angle of 37.0 degree with the horizontal , as shown in Fig. 3 - 35. (a) Determine the time taken by the projectile to hit point P at ground level. (b) determine the range X of the projectile as meassured from the base of the cliff. At the instant just before the projectile hits point P, find (c) the horizontal and the vertical components of its velocity. (d) the magnitude with teh horizontal (f) Find the maximum height above the cliff top reached by the projectile.

im conenctrating on (a) right now and cant seem to find the answer T_T

heres Fig 3-35 drawn on paint :T_T:

oh btw if anyone has the Physics book by Giancolli 6th edition, its page 66 number 31.

[Image: http://img834.imageshack.us/img834/7147/apainn.png]

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please show which formula you used btw please and thank you :worry:
Justified wrote on 2010-09-17 01:45

a = -9.8
v = -9.8 t + 65sin(37)
p = -4.9 t^2 + 65sin(37) t + 125

Solve for -4.9 t^2 + 65sin(37) t +125 = 0.

Edit: t = 8.5 seconds

First, separate the initial velocity into both X and Y (length and height) components using the angle. Length and Height are independent of each other, so just calculate when Y hits the ground (position = 0, or displacement = -125).

I'm not sure if my math was right, both Calculus and Physics were more than 3 years ago for me.
Q wrote on 2010-09-17 01:52

isnt he velocity 65m/s though?

and bleh the answer is wrong, its suppose to be 10.4 but i dont understand how to get there T_T?
Arsik wrote on 2010-09-17 01:56

Moving to The Library, since that's the place for logical and intelligent discussions. And since homework usually requires intelligent thought, I'm moving it there. Also don't doublepost.
Q wrote on 2010-09-17 01:59

oh sorry and kk ill remember to post on library next time. still new to the system lol.
pkMaster wrote on 2010-09-17 02:12

No, his calculation is correct. Though I'm not sure how he got 8.5 seconds when I got 10.4 . My guess is that he was doing the calculation in radians, not degrees.
Justified wrote on 2010-09-17 02:17

Quote from pkMaster;158502:
No, his calculation is correct. Though I'm not sure how he got 8.5 seconds when I got 10.4 . My guess is that he was doing the calculation in radians, not degrees.

I have no physical calculator. Being the lazy person I am, I chose to throw it at an online graphing calculator instead of step-by-step on the Windows calculator and I guess they botched it.

At least I can stop trying to find where I screwed up now.
Taycat wrote on 2010-09-17 02:19

This reminds me of Geometry because we had to figure things out at angles and whether they were climbing or falling.