One 110 kg football lineman is running to the right at 2.75 m/s while another 13

Question

One 110 kg football lineman is running to the right at 2.75 m/s while another 135 kg lineman is running directly toward him at 2.80 m/s .

What is the magnitude of the net momentum of these two athletes? What is their total kinetic energy?

Two identical 1.80 kg masses are pressed against opposite ends of a spring of force constant 1.55 N/cm , compressing the spring by 15.0 cm from its normal length.

Find the maximum speed of each mass when it has moved free of the spring on a smooth, horizontal lab table.

Explanation / Answer

net momentum is (110*2.75)-(135*2.8) =-75.5 kg*m/s

total KE = 0.5*m1*v1^2 + 0.5*m2*v2^2 = (0.5*110*2.75*2.75)+(0.5*135*2.8*2.8) = 945.13 J

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energy stored in the spring is 0.5*k*x^2 = 0.5*155*0.15*0.15 =1.74 J

this is equally shared by each ball

then KE of each ball is 1.74/2 = 0.87 J

0.5*m*v^2 = 0.87

0.5*1.8*v^2 = 0.87

v = 0.98 m/s

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