I remember
http://www.jiskha.com/display.cgi?id=1448486880
Alex is exploring a cave that has a slight incline and is iced over, forcing her to use ice cleats to explore it. After climbing 50 m into the cave, she finds what she is looking for and she takes out her ice pick and hammer to begin removing the stones. Little does she know her hammering has triggered a rock slide 100 m into the cave, releasing a large boulder to slide down the icy incline with no friction. The boulder is released from rest and accelerates down toward her at a constant rate of 0.85 m/s2. She doesn’t notice this until the boulder is only 25 m away from her. Reacting quickly, she pushes herself down the incline towards the cave entrance, knowing the boulder is too large to fit through it. Remembering what she learned in physics, she knows she will accelerate down the inline with the same acceleration as the boulder, thanks to the frictionless surface created by the ice.
(d) Now since Alex has escaped the cave, she has a new problem. She is sliding towards a cliff that is 10 m away from the cave entrance. The good news is, she is no longer speeding up, but instead slowing down due to friction. Based on your previous answers, how fast is she moving when she escapes the cave?
(e) Using the fact that the static and kinetic coefficients of friction are 0.75 and 0.5, respectively, will she slow down in time and live or will she plummet to her death? Prove your answer mathematically by showing how far she will slide and compare it to the 10 m mentioned above. And no, you do NOT need to know her mass.
Assume she is sliding on a horizontal surface.
If anyone can help solve or explain the problem, I would greatly appreciate it!
4 answers
from before:
She must do 50 meters in 7.67 seconds with starting speed v and acceleration of .85
50 = v (7.67) + (1/2) .85 (7.67)^2
50 - 25 = 7.67 v
v = 3.26 m/s starting speed
NOW ::::::
v = 3.26 + .85 (7.67)
= 9.78 m/s as she pops out into the sun
She must do 50 meters in 7.67 seconds with starting speed v and acceleration of .85
50 = v (7.67) + (1/2) .85 (7.67)^2
50 - 25 = 7.67 v
v = 3.26 m/s starting speed
NOW ::::::
v = 3.26 + .85 (7.67)
= 9.78 m/s as she pops out into the sun
we need the kinetic friction
work done by friction = initial Ke
mu m g x = (1/2) m v^2
.5 (9.81) x = 9.78^2 / 2
x = 9.75 meter slide
well, she made it !
work done by friction = initial Ke
mu m g x = (1/2) m v^2
.5 (9.81) x = 9.78^2 / 2
x = 9.75 meter slide
well, she made it !
Thank you so much!!
2 answers