Homework Help: physics

Posted by john on Sunday, January 22, 2012 at 2:48pm.

A rocket moves straight upward, starting from rest with an acceleration of +25.5 m/s2. It runs out of fuel at the end of 4.26 s and continues to coast upward, reaching a maximum height before falling back to Earth.
(a) Find the rocket's velocity and position at the end of 4.26 s.
vb = m/s
yb = m

(b) Find the maximum height the rocket reaches.
m

(c) Find the velocity the instant before the rocket crashes on the ground.
m/s

physics - Henry, Wednesday, January 25, 2012 at 2:32pm
a. Vf=at=25.5 m/s^2 * 4.26s=10=108.6m/s
h=0.5a*t^2 = 0.5*25.5*(4.26)^2=231.4 m

b. hmax = (Vf^2-Vo^2) / 2g,
hmax = (0-(108.6)^2)/ -19.6 = 601.7 m.

c. Vf^2 = Vo^2 + 2g*d ,
Vf^3 = 0 + 19.6*601.7 = 11793.3,
Vf = 108.6.

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