What is the inital speed of the ball?

[yankee]

A ball player hits a home run and the baseball just clears a wall8.00m high located 142.0m from a home plate. The ball is hit at an angle of 40degrees to the horizontal and air resistance is negligible. Assume the ball is hit at a height of 1.1m above the ground. The acceleration of gravity is 9.81m/s^2. What is the inital speed of the ball?

 

[HallsofIvy]

Oh, come, on. Try. The vertical acceleration is -9.8 m/s² and there is no horizontal acceleration. Taking v as the initial speed (what you want to find), the initial horizontal speed is v cos(40) and the initial vertical speed is v sin(40). Now find the horizontal and vertical speed functions, v_x(t) and v_y(t), and the horizontal length and vertical height functions, x(t) and y(t). When the ball passes over the the wall, you have x(t)= 142 and y(t)= 8. That gives you two equations for the two "unknowns", t and v.