Mary (mass - 33 kg) likes to slide. On a playground there is a straight metal sl
ID: 2034684 • Letter: M
Question
Mary (mass - 33 kg) likes to slide. On a playground there is a straight metal slide with a vertical drop of 2.0 m and a length (measured along the slide) of 3.3 m. Suppose she starts from rest at the top of the slide and has a speed of 2.7 m/s when she reaches the bottom. (a) What was the net change in potential energy when she went from the top of the slide to the bottom? And what was the change in her kinetic energy? Be sure to indicate the correct signs (positive or negative) (b) What was the net change in the thermal energy of the slide and the seat of her pants due to friction between her pants and the slide? (Hint: this is simply the work done by friction- the materials sliding against each other shake up the atoms near the surfaces, and that represents thermal energy which then spreads further into the materials.) (e) Using this information, determithoicet of kinetic friction between her pants and the slide.Explanation / Answer
a)
Change in Potential energy
dU=Uf-Ui =mghf-mghi =33*9.81*(0-2)
dU=-647.46 J
Change in Kinetic energy
dK=Kf-Ki =(1/2)m(Vf2-Vi2) =(1/2)*33(2.72-0)
dK=120.285 Joules
b)
Net change in thermal energy
dE =647.46-120.285
dE=527.175 Joules
c)
o=SIn-1(2/3.3)=37.3o
Work done by friction
W=umgdCos(o) =527.175 J
u*33*9.81*3.3*Cos37.3 =527.175
u=0.62