1-An elevator cab and its load have a combined mass of 2000kg. 1600kg of this ma
ID: 2242054 • Letter: 1
Question
1-An elevator cab and its load have a combined mass of 2000kg. 1600kg of this mass belong to the elevator and 400kg belong to the load. What force dose the load exert on the floor of the elevator if the elevator, which is initially moving at a speed of 10m/s, is brought to rest in a distance of 40m?
2- A father racing his son has 2/3 the kinetic energy of the son who has 2/3 the mass of the father. The father increases speed by 1.0m/s and then has the same kinetic energy as the son. What is the origianal speed of the father?
Explanation / Answer
2)
now given originally, KE(father)=(2/3)KE(son)
(1/2)m(f)v(f)^2=(2/3)(1/2)m(s)v(s)^2
=(1/2)(2/3)(2/3)m(f)v(s)^2
v(f)^2=(4/9)v(s)^2
after the father speeds up to 1m/s,KE(father)=KE(son)
(1/2)m(f)v(f)^2=(1/2)m(s)v(s)^2
=(1/2)(2/3)m(f)v(s)^s
v(f)^2=(2/3)v(s)^2
1=2/3 v(s)^2
v(s)=root(3/2)=1.225m/s
substituting in v(f)^2=(4/9)v(s)^2
v(f)=0.82m/s
1)
a =v^2/2d =10*10/(2*40)=1.25 m/s2
mg-N=ma
==> N=m(g- a)=400*(9.8 -1.25)
N=3420N
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