I need help...I am not so good at physics...can someone help?

Question

Here's the problem:
A bowling ball 25 cm in diameter is slid down an alley with which it has a coefficient of sliding friction of µ = 0.55. The ball has an initial velocity of 9 m/s and no rotation. g = 9.81 m/s2. Note: For a sphere Icm = (2/5)mr2

a) What is the initial deceleration of the ball?
b) What is the initial angular acceleration of the ball?
c) How long does it take before the ball starts to roll without slipping?
d) If it had been moving 11.7 m/s initially, how long would it have taken the ball to start rolling without slipping?

Answer 1

(a) F>=f
F=ma
f= µ mg
ma>=µ m g
a>=µ g= 0.55 x 9.81=5.4m/s^2

(b) T=Icm A
T= rF
A=rF/Icm
A= r m a /(2/5)mr^2
A= 5a/ 2r = 5 x 5.4m/ ( .25)=108 rad/s^2

(c) F<=f
a<= 5.4 m/s^2
Energy equation
Ke(initial) - W(work done by friction)=Ke(when it starts rolling)
0.5 mV(0)^2 - µ mg S = 0.5 mV(t)^2
V(0)= 9 m/s
V(t)=V(0) - at and
S= V(0)t - 0.5 a t^2
Substitute S and V(t) into energy equation and solve for t.

(d) same as (c) only V(0)=11.7 m/sec