Ballistic free-fall - rock slide

[gremmie]

Homework Statement

At 6:52 pm PDT Wednesday, July 10, 1996, a large block of granite with an estimated volume of 78,000 cubic yards detached from the cliff between Washburn Point and Glacier Point in Yosemite Valley. The estimated mass of the granite is 80,000 metric tons. Rock falls are a natural and continuous process on the granite cliffs in Yosemite Valley, however, most of the falls result in rock slides. This fall was unique in that it resulted in a projectile type of ballistic free-fall.

Shown on the last page is a profile of the fall. The rock mass slid down the rock shelf and went into the projectile motion seen in the diagram.

Use the profile and what you have learned about projectile motion to answer the following questions:

a. Use information about the rock shelf (see diagram) to determine the launch angle at the point where the rock mass went into projectile motion

b. Write the components of the rock’s velocity at the point where it went into projectile motion in terms of the initial launch angle and

c. Calculate the time the rock was in the air

d. Calculate the horizontal and vertical components of the rock’s velocity the instant before it struck the ground (final velocity components and )

Homework Equations

Kinematics equations

The Attempt at a Solution

Im stuck ... my knowns are y_0= 1750 and x_f = about 350... i tried to get time by using height = 1/2 gt^2... but it seems like there is an initial velocity of the slide that i need to find time if I am going to use y_f = y_o + v_i(t) -1/2(g) t^2 to find time.. or if I am going about it the wrong way let me know..thanks

 

[ashishsinghal]

You are going the right way.
But here we have got two equations with three variables. Maybe they want you to obtain the angle by measuring it on the image above. Not sure though.