A thrill-seeking cat with mass 4.00 kg is attached by a harness to an ideal spri

Question

A thrill-seeking cat with mass 4.00 kg is attached by a harness to an ideal spring of negligible mass and oscillates vertically in SHM. The amplitude is 0.050 m , and at the highest point of the motion the spring has its natural unstretched length. Calculate the elastic potential energy of the spring (take it to be zero for the unstretched spring), the kinetic energy of the cat, the gravitational potential energy of the system relative to the lowest point of the motion, and the sum of these three energies when the cat is

a. Calculate the elastic potential energy of the spring (take it to be zero for the unstretched spring) when the cat is at its lowest point.

b. Calculate the kinetic energy of the cat when the cat is at its lowest point.   

c. Calculate the gravitational potential energy of the system relative to the lowest point of the motion when the cat is at its lowest point.

d. Calculate the sum of these three energies when the cat is at its lowest point.

Explanation / Answer

(a)

the elastic potential energy of the spring is

PE = mgh= 2mg A = 2 ( 4)( 9.8)(0.050) = 3.92 J

(b)

The total energy at the lowest point h= 0

PE = mgh = mg (0) =0

v = 0 so KE = 0

PE = 1/2 k x^2

= 3.92 J

(c)

at equlibrium the total energy is

PE = TE/4 =3.92 J/4=0.98 J

gravitational potential energy PE_ grav = 3.92/2 = 1.96 J

kinetic energy is 0.98 J

(d)

TE = PE_grav+ PE + KE = 3.92 J

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