Ok i tried these questions over and over and i cannot seem to grasp the idea so if someone could please just give me the full answer to this it would be greatly appreciated so i can see fully how to do it and i can apply it to similar questions... 1. a) Cathy takes the bus home from work. In her hand she holds a 2.0 kg cake box, tied together with string. As she ascents the steps into the bus, the box accelrates upward at a rate of 2.5 m/s^2. What is the force exerted on the string? (ok is this a tention question or how do i do this, can anyone prove an explanation or a full answer? ) b) Cathy sets the box on the seat beside her. the bus accelrates from rest to 60 kn/h in 4.0s, and the box begins to slide. What is the coeffiecent of static friction between the box and the seat of the bus? (ok i know that Ff=Us(Fn) I know Fn = ma i know a=v2^2-v1^2/2d i found d by doing .5(v1 + v2)(t) so i can find accelration i find Fn = m which is 2 kg and acelartion which i believe is 4.1675 m/s^2 but i am left with a equation iwht 2 variables Ff=Us(Fn), Therfore Us = Ff/Fn i know Fn but i do not know Ff, please someone enlighten me) c)A taxi suddnelt cuts in front of the bus, causing the bus driver to slam on the brakes. The bus driver reduces speed from 60km/h to 20km/h in 1.5s. Does Cathy's cake slide forward? (is this Uk??? i need major help with this one, this is accelration isnt it?) Ok Next question...I have to design and complete an investigation to determine how the folloing factors affect the force of friction: wieght Surface area speed I need to measure the magnitude of the force of friction. any suggestions on how i should go about this? Please help me PLEASE i am taking sorrespondant physics during my summer break and it is really hard i have no teacher and no background in physics, PLEASE help.