Yes.
I don't quite understand what you wrote down here.
Because it is an elastic collision momentum will be conserved. What does the formula for conservation of momentum look like? Which variables will be 0 (and there for contribute to 0 momentum) before and after the collision?
These centripetal force questions are rather difficult to visualize, so here maybe one of the diagrams here will help you a bit: http://hyperphysics.phy-astr.gsu.edu/hbase/corf.html
For the second question:
You're on the right track thinking about conservation of energy. What will define the energy of the system at the moment the block is dropped? What will define the energy of the system after it has dropped and compressed the spring?
You must find out how long it takes the SOUND to travel 17m (make sure to correct for the temperature), and then add that to the time it takes for the LIGHT to travel 75,000km. Compare that to the time it takes the sound to travel 140m to the outfield bleachers.
Okay, although this problem involves some rather boring and tedious math, the answer is achieved by simply using the kinematic equations as all this is is a projectile motion problem.
Having quick equations like altamashghazi suggested is nice, but knowing how to get them is always the best...
Unless I've made a terrible mistake in my calculations, it seems as though either the question gave you a wrong number for the length of the string, or somehow the ball will go above the height of the pendulum, even though there is a ceiling in the way.
Right. y=0, which is the position where the ball is hanging, to the position where the ball is at a max height. One would assume that to create an equation relating this height to the distance between the ball and the ceiling, you would need to have the variable L somewhere in the equation you...
Forget what I said, I misread/misunderstood your explanation. Yes, energy is conserved here.
When you are calculating h from the potential energy equation, what does h represent?
Shlurpie,
A piece of advice, unrelated to the solution to this problem, is that you need to look at the units of your calculations.
It looks to me as though you tried to calculate the force of gravity in the y direction, but your force would've had units of only Kg.
F=m*a= kg*m/s2...
Looks correct. As for the rounding, it's best to ask your teacher/professor what they prefer because they all seem to have their own favourite way. Some may want significant figures, some want 3 decimal places always.