Sample problem 13-2 AK+△O+△Emt=Wa A 4.5 kg block is thrust up a 30 incline with an initial speed v of 5.0m/s. It is found to travel a distance d=1.5 up the plane as its speed gradually decreases to zero plane Earth gain in this process due to friction?x How much internal energy does the system of block Solution: System block t plane t Earth, ignore the kinetic energy changes of the Earth △Emt=-(△U+△K) △U=U-1=(m8)-0= mgd sin30=33y △K=Kr-K1=0-m 56J 2 →AEn=-(△U+△K)=23J Ch 13 Energy III: Conservation of energyCh.13 Energy III: Conservation of energy Sample problem 13-2 A 4.5 kg block is thrust up a incline with an initial speed v of 5.0m/s. It is found to travel a distance d=1.5 m up the plane as its speed gradually decreases to zero. How much internal energy does the system of block + plane + Earth gain in this process due to friction?  30 Solution: System = block + plane + Earth, ignore the kinetic energy changes of the Earth. ( ) Eint = − U + K K + U + Eint = Wext U U U mgh mgd J  = f − i = ( ) −0 = sin 30 = 33  K K K m v J f i 56 2 1 0 2  = − = − = − E ( U K) 23J  int = −  +  =