physics
posted by Elisa .
1. A 10.0 g object moving to the right at 25.0 cm/s makes an elastic headon collision with a 15.0 g object moving in the opposite direction at 36.0 cm/s. Find the velocity of each object after the collision.
10.0 g object:
15.0g object:
2. A dentist's drill starts from rest. After 3.00 s of constant angular acceleration it turns at a rate of 2.00 multiplied by 104 rev/min.
(a) Find the drill's angular acceleration.
(b) Determine the angle (in radians) through which the drill rotates during this period.

well since everything is in cm and seconds and grams we can stay in the centimeter, gram, second or"cgs" units.
Initial momentum = 10*25  15*36
= 290 (to the right is positive)
final momentum =same = 290 = 10 U + 15 V
elastic so initial KE = final KE
(1/2) 10 (625) + (1/2) 15 (1296)
3125+9720
=12,845 dynes
final KE =12,845 = 5 U^2 + 7.5 V^2
so two equations, two unknowns:
290 = 10 U + 15 V
12,845 = 5 U^2 + 7.5 V^2
U =  (1.5 V + 29)
U^2 = 2.25 V^2 + 87 V + 841
12,845 = 5(2.25 V^2 + 87 V + 841) + 7.5 V^2
You can solve the quadratic I think 
in 3 seconds from 0 to 2*10^4 revs/min
first change rev/min to radians/sec
2*10^4rev/min (1 min/60 s)(2 pi rad/rev)
=2094 radians/s
alpha = change in speed/change in time = 2094/3 = 698 radians/s^2
angle = (1/2) alpha t^2
=349*9 = 3141 radians
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