Homework Help: PHYSICS - PLEASE HELP

Posted by Mary on Wednesday, November 28, 2012 at 7:45am.

Part A:
A cardinal (Richmondena cardinalis) of mass 4.50×10^−2 kg and a baseball of mass 0.142 kg have the same kinetic energy. What is the ratio of the cardinal's magnitude p(c) of momentum to the magnitude p(b) of the baseball's momentum?

Part B:
A man weighing 650 N and a woman weighing 460 N have the same momentum. What is the ratio of the man's kinetic energy K(m) to that of the woman K(w)?

PHYSICS - PLEASE HELP - Henry, Friday, November 30, 2012 at 7:38pm
A. 0.5Mc*Vc^2 = 0.5Mb*Vb^2.
0.5*0.045*Vc^2 = 0.5*0.142*Vb^2
0.0225(Vc)^2 = 0.071(Vb)^2
Vc^2 = 3.156Vb^2.
Vc = 1.77Vb

Mc*Vc/Mb*Vb
Replace Vc with 1.77Vb:
Mc*1.77Vb/Mb*Vb
0.045*1.77Vb/(0.142*Vb
0.07965Vb/0.142Vb = 0.561 = Momentum of
Cardinal/Momentum of baseball.

B. m1*g = 650 N.
m1=650/g=650/9.8 = 66.3 kg.=Mass of man

m2*g = 460 N.
m2=460/9.8 = 46.94 kg. = Mass of woman.

m1*V1 = m2*V2.
66.3V1 = 46.9V2
V2 = 1.414V1.

K1/K2 = 0.5m1*V1^2/0.5m2*V2^2
K1/K2 = 0.5*66.3*V1^2/0.5*46.9*V2^2
K1/K2 = 33.15V1^2/23.45V2^2
Replace V2 with 1.414V1:
K1/K2 = 33.15V1^2/23.45*(1.414V1)^2
K1/K2 = 33.15V1^2/46.9V1^2 = 0.707.

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