# Projectile motion with mass height and range

1. Jun 26, 2013

### SPiazzo

Hello all I have a question I was hoping someone could answer for my homework.
A 78.0-kg boulder is rolling horizontally at the top of a vertical cliff that is h1 = 16 m above the surface of a lake, as shown in the figure below. The top of the vertical face of a dam is located d = 110 m from the foot of the cliff, with the top of the dam level with the surface of the water in the lake. A level plain is h2 = 28 m below the top of the dam.
a) What must be the minimum speed of the rock just as it leaves the cliff so it will travel to the plain without striking the dam?
b) How far from the foot of the dam does the rock hit the plain?

from what I could find on Google about it, it seems to be a conservation of energy problem as that is the only way you can relate mass to anything. As all of the kinematic equations I have seen in my book and notes have no variable for mass. I am also fairly certain that the limited amount of information in the problem means that the mass is simply not there for no reason.

2. Jun 27, 2013

### tiny-tim

Welcome to PF!

Hello SPiazzo! Welcome to PF!
No, just use the standard constant acceleration equations.

3. Jun 27, 2013