1. A father racing his son has 1/2 the kinetic energy of the son, who has 1/2 th
ID: 1777190 • Letter: 1
Question
1. A father racing his son has 1/2 the kinetic energy of the son, who has 1/2 the mass of the father. The father speeds up by 1.6 m/s and then has the same kinetic energy as the son. What are the original speeds of (a) the father and (b) the son?
2.The roof of a large arena, with a weight of 500 kN, is lifted by 44 cm so that it can be centered. How much work is done on the roof by the forces making the lift? (b)In 1960 a Tampa, Florida, mother reportedly raised one end of a car that had fallen onto her son when a jack failed. If her panic lift effectively raised 4000 N (about 1/4 of the car's weight) by 5 cm, how much work did her force do on the car? Answer should be Jolus.
Explanation / Answer
Q1
Given data
M = mass of father
m = mass of son
Vi = speed of father before
Vf = speed of father after
v = speed of son
1/2 M = m
Vf = Vi + 1.6
KE[father before] = ½*M*Vi2
KE[son] = ½ *m*v2
KE[father after] = ½*M*Vf2
a)
KE[son] = KE[father after]
½*M*Vf2) = ½*m*v2
½*M*Vf2 = ¼*M*v2
Vf2 = ½*v2
20.5*Vf = v
Vi + 1.6 = v/20.5 ……………eq1
½*M*Vi2 = ½*( ½*m*v2)
M*Vi2 = ½* ½ *M*v2
Vi2 = ¼*v2
Vi = ½v ……………eq2
solve eq1 and eq2
0.5v + 1.6 = v/20.5
0.5v + 1.6 = 0.7071v
v = 7.72 m/s2
Vi = 3.86 m/s2
Q2.
W=F*D
a)
W = 500000N*0.44m
W=220000J
b)W=4000N*0.05m
W=200J
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