How far is HOLY HILL from PORTAGE?

How long( time in seconds) does it take the child to reach the hill bottom?

• A 35 N child gives her 10 N sled an initial velocity of 2 m/s and then slides down a 55 m hill with 15° angle of elevation. If the coefficient of kinetic friction between the hill and the sled is .1, how long does it take the child to reach the hill bottom? answer is 7.15s not sure how to do this problem,, do you change the newtons of child and sled to mass and assume velocity final is 0? Please help, and thank you!

• Answer:

  Energy conservation method : 1) energy E at start U = mgh = 45*55 = 2475 J K = 1/2m*Vo^2 = 45/19.6*4 = 9.2 J E = U+k = 2420+9.2 = 2484.2 2) Energy lost while sledding because of friction Er = E*μ = 2484.2*0.1 = 248.4 J 3) energy Edh at the bottom of the hill Edh = E-Er =2235.8 J 4) Final speed Vdh at the bottom of the hill Vdh = √2Edh*g/F = √973.80 = 31.21 m/sec D = 55/sin15° = 212.5 m 425 = (2+31.2)*t t = 425/33.2 = 12.80 sec Your answer is wrong !!!