- #1
Wes Turner
- 66
- 14
Homework Statement
A child goes down a water slide. The slide is 9.0 m tall. She pushes off with an initial speed of 2.0 m/s (in the horizontal direction). If the slide is frictionless, how fast will she be going at the bottom of the slide?
Homework Equations
In the book, they use a conservation of energy equation:
K + Ug = K0 + (Ug)0
The Attempt at a Solution
(1/2)*m*v^2 + mgy = (1/2)*m*v0^2 + mgy0
Since y = 0, we have
(1/2)*m*v^2 = (1/2)*m*v0^2 + mgy0
Solving for v1, we get
v1 = sqrt(v0^2 + 2gy0)
v1 = sqrt((2.0 m/s)^2 + 2(9.8m/s^2)*(9.0m)) = 13 m/s
My problem is that the only force here is gravity and it is in the x direction, but the increase in velocity is in the orthogonal y direction. I understand that the normal force from the slide pushes the child in the x direction, but why is it not necessary to break all that down into x and y components? It seems like gravity is acting perpendicular to the vertical.