# Determine the speed with which he must throw the ball

#### evilphysics

Being the overachiever I am, i decided to take a summer course in physics to get ahead of the game... BAD IDEA. I'm really struggling with some things in this class, homework in particular. I can answer the examples in the book well, but when i am left to answer the actual questions i feel it's in another language. These are out of Physics, 7th Ed Cutnell:

1) A quarterback claims he can throw the football a horizontal distance of 183m (200yd). Furthermore, he claims that he can do this by launching the ball at 30 degrees above horizontal. Determine the speed with which he must throw the ball. Assume the ball is launched and caught at the same vertical level and ignore air resistance. For comparison, a baseball pitcher who can accuratly throw a fastball at 45 m/s (100 mph) is exceptional.

I started by drawing a diagram. I also worte out the variables as follows:
Initial V = 0 A = G = -9.8 m/s^2
V = ? X = 183 m
I then used the equation V^2 = Vo^2 + 2ax which corrisponds to:
V^2 = -4000. I took the square root of this and I came out with 63.2 m/s. Can anyone Varify?

2)Two cars A and B are traveling in the same direction, although car A is 186m behind car B. The speed of A is 24.4 m/s and the speed of B is 18.6 m/s. How much time does it take for A to catch B?

I didn't even know where to start on this question.

3)A car drive straight off a cliff that is 54m high. The police at the scene of the accident observe that the point of impact is 130m from the base of the cliff. How fast was the car travling?

Once again i don't know where to start with this equation either.

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#### CaptainZappo

Please post in the correct forum; there is a section devoted specifically to homework help.

#### CaptainZappo

For question 1, you must break the velocity into components (horizontal and vertical). Gravity only affects the vertical component of velocity; use this to your advantage.

For question 2, write the position of each car as a function of time. This should not be too hard as you know the velocity of each car.

For question 3, recall that gravity only affects the vertical component of velocity. How long does it take an object to fall from 54 m? What does this tell you about the horizontal component of velocity?

I hope this is of some help.

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