1. Suppose a crate of mass 2.4 kg is placed on the plank in the figure below at
ID: 1545720 • Letter: 1
Question
1. Suppose a crate of mass 2.4 kg is placed on the plank in the figure below at a distance x = 7.6 m
from the left end. If the plank has a mass of 12 kg, find the forces exerted by the two supports on the plank. (Indicate the direction with the sign of your answer.)
2. Consider a roller coaster that moves along the track shown in the figure below. Assume all friction is negligible and ignore the kinetic energy of the roller coaster's wheels. Assume the roller coaster starts with a speed of 13 m/s at point A. Find the speed of the roller coaster when it reaches locations B and C. (Assume hA = 28 m and hB = 14 m.)
vB
vC
vB
= m/svC
= m/sExplanation / Answer
2) KE(A)+PE(A)=KE(B)
mv(A)²/2 +mgh(A)= mv(B)²/2
v(B)=sqrt[v(A)²+2gh(A)] =
=sqrt[13²+2•9.8•28) =26.79 m/s
KE(B)+PE(B)=KE(C)
mv(B)²/2 +mgh(B)= mv(C)²/2
v(C)=sqrt[v(B)²+2gh(B)] =
=sqrt[26.79²+2•9.8•14) =31.5 m/s
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