killswitch9 (killswitch9) wrote in istupidneedhelp,

physics confusion

the following are four problems that have been giving me trouble. i often don't know where to start with these physics problems due to the fact that i can't find the correct formula(s) to use. any help would be greatly appreciated. thanx in advance!

1) a small cube slides down a frictionless incline. it then strikes elastically another cube at the bottom that is only 1/4 of its mass. if the incline is 30m high and the table is 100cm off the floor, where does each cube land?

2) a shop sign weighing 215N is supported by a uniform 135N beam.
a)find the tension of the cable and the reaction forces exerted at the hinge.
b) if someone were to cut the cable, what angular acceleration will the beam experience at the instant the cable is cut?

3) a baseball just clears a 3m wall which is 120m from home plate. if the ball leaves the bat at 45 degrees and 1.2m above the ground, what must its initial velocity be? assume no air resistance.

4) a 900kg object strikes a huge spring at a speed of 20m/s, compressing it 5m.
a) what is the spring constant?
b) how long is the object in contact with the spring before it bounces off in the opposite direction?

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