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"First,let us draw a velocity-time graph."First,let us draw a velocity-time graph.
"Area under velocity-time graph gives object's displacement."Area under velocity-time graph gives object's displacement.
180=((8+4))/2*t" , "180=12/2*t" , "t=30 "sec"180=(8+4)2⋅t , 180=122⋅t , t=30sec
"The slope of velocity-time graph gives deceleration of object."The slope of velocity-time graph gives deceleration of object.
tan alpha=(4-8)/30=-4/30=-2/15" "m/s^2tanα=4−830=−430=−215 ms2
"We can calculate the friction force between contacted surface "We can calculate the friction force between contacted surface "using formula " F_f=k*Nusing formula Ff=k⋅N
"Where "F_f ":The friction force , k:coefficient of friction force ,"Where Ff:The friction force , k:coefficient of friction force ,
"and N: Normal Force."and N: Normal Force.
"Note that N="m*gNote that N=m⋅g
F_f=k*m*gFf=k⋅m⋅g
"according to Newton's second law of Dynamics "F=m*aaccording to Newton's second law of Dynamics F=m⋅a
"Thus , we can write as "m*a=k*m*gThus , we can write as m⋅a=k⋅m⋅g
"Let us simplify "cancel(m)*a=k*cancel(m)*g
"We get "a=k*g
k=a/g
k=2/(15*9.81)
k=0,013591573
k~=0.0136
