help with remaining physics questions? :)

Question

anonymous · Answer

a stone attached on a rope. That stone performs a uniform circular motion with a radius of 1 ~ m The stone makes one revolution per second. The average acceleration of the stone during 1/4 revolution is? step by step answer please

anonymous · Answer

@ajprincess  @tuna  @supercrazy92 @kropot72

anonymous · Answer

i'll post how someone had previously answered it but there explanation was lacking :/ http://openstudy.com/users/bronzegoddess#/updates/4fde1323e4b0f2662fd32a0b

anonymous · Answer

anyway..maybe i'll continue onto next question?

anonymous · Answer

two trees are connected by a tight string. a person pulls in the middle of the string with a force of 50N so that the angle between the string and the connecting line of the trees is 15°, what is the tension in the string?|dw:1340786588590:dw||dw:1340786629008:dw| idk where the angle should be.
A.50N  B.50N/sin15°  C.50N/2sin15°  D.50N/2cos15°