4) What was Alhazen’s greatest contribution to science? 5) What is the name of the only particle that can travel at the speed of light?

7) What did William Herschel’s experiment with light and heat prove?
8) Why are organ pipes in the Abbey different lengths?
9) What is the difference between light and sound waves as they travel?
10) Which color has the lowest amount of energy, and why?
11) Why are there dark bands in the spectra Joseph Fraunhofer saw?
12) What did Joseph Fraunhofer discover about the elements that make up the universe? only his tent, a piece of wood, and a ruler?

Astudent throws a water balloon with speed v0 from a height h = 1.76 m at an angle θ = 21° above the horizontal toward a target on the ground. the target is located a horizontal distance d = 9.5 m from the student’s feet. assume that the balloon moves without air resistance. use a cartesian coordinate system with the origin at the balloon's initial position. (a) what is the position vector, rtarge t, that originates from the balloon's original position and terminates at the target? put this in terms of h and d, and represent it as a vector using i and j. (b) in terms of the variables in the problem, determine the time, t, after the launch it takes the balloon to reach the target. your answer should not include h. (c) create an expression for the balloon's vertical position as a function of time, y(t), in terms of t, vo, g, and θ. (d) determine the magnitude of the balloon's initial velocity, v0, in meters per second, by eliminating t from the previous two expressions.