physics. CONFUSING!?

Question

A 55 kg trampoline artist jumps vertically upward from the top of a platform with a speed of 5.0 m/s. (Ignore small changes in gravitational potential energy.)


(a) How fast is he going as he lands on the trampoline, 3.0 m below?
___ m/s
(b) If the trampoline behaves like a spring of spring constant 5.2 104 N/m, how far does he depress it?
___m





A 0.590 kg wood block is firmly attached to a very light horizontal spring (k = 200 N/m) as shown in Fig. 6-40. It is noted that the block-spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?





can anyone do any of that?!?!?

Answer 1

a) using conservation of energy

.5*m*5^2+m*9.8*3=.5*m*v^2
solve for v
v=9.15 m/s

b) again with the energy
0=-.5*55*9.15^2-.5*55*x+.5*52000*x^2
solve for x
x=0.298 m



Question #2:

The energy stored in the spring is
.5*k*x^2
when compressed
.5*200*(5/100)^2
when elongated
.5*200*(2.3/100)^2

the difference is the energy lost to friction for the block to slide 7.3 cm

the energy of friction is
0.590*9.81*µk*7.3/100
solve for µk

µk=0.466

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