Monday 11 Oct:

You Keep the Free Response Q's in a folder!

Journal:

Two cords suspend a 39.0 kg block A equally. An 18.0 kg plate is suspended equally by two other cords connected to the block that each makes an angle of 24.0^o with the bottom of the block.

Finally a 4.70 kg bob is hung from the bottom of the plate

(A) What is the net force

 on the 18Kg plate?
 

(B)  What is the tension in either cord B?
(C) If cord C were cut, what would be the tension in either cord A?
 

A:SF = 0

b.   SF = 0 

Y-direction: 

2(sin24⁰T) = (mg of 18-kg) + (4.7-kg) plates

       2(sin24⁰T)   = 180N + 47N  = 227N  

       2(.407T)    =    227N         

                  T    =    279N  

c.  2(sin24⁰T) = (mg of 18-kg+ (39-kg) )

     2T   = 570N

         T    =    285N

Quiz Today:  #1 Free Response

Quiz Wed:  #2 Free Response

Equation Test on Fri 15 Oct

Test on Mon/Tues 18/19 Oct

Quiz (Equations 1-18a, 41-44) :    

Name _________________________________

1.      (Velocity after a period of time)

V_f=

2.      (Distance after a period of time)

X_f =

3.     (Velocity/distance/acceleration without time)

V_f²            =

4.       (center seeking acceleration or centripetal acceleration)

A_c=

5.     Work in relationship with KE + PE (usingfundamental terms)

W  =

6.      (Change of momentum (Dr )=  Impulse)

=

7.      (Power with work)

P_avg =

8.      (Power with veolcity)

P =

9.      (Force exerted by a springy)

F_s =

10.  (Potential energy of a spring)

U_s =

11.  (period of a spring)

T_s =

12.  (period of a pendulum)

T_p =

13.  (relationship between period and frequency)

T =

14.  (Newton’s Law of Gravitation)

F_g =

15.  Pressure (with atmosphere) of a liquid

    P =

16.  (Force of buoyancy)

F_buoy =

17.  (Equation of continuity for a liquid)

A₁V₁ =

Q: a. How much work is required to stop a 80 kg mass be moving at 11.2m/s?

b. If it takes 2.0 m to stop it, what force is applied?

c. What is the impulse?

d. How much time does it take?

ans:  a.  W = DKE + DPE= 1/2 mV² + 0

           5000J = (.5)(80kg)(11.2m/s)²
            W =  5,000J

b. W = (f)(x)   -->  5,000J = f(2m)

                             f = 2,500N

c. Impulse = DMomentum

         (f)(t) = m(DV)

      Impulse = (80-kg)(11.2m/s)

       Impulse = 896 Ns

    d.   Impulse = DMomentum

         (2,500)t = 896 kgm/s

               t = 0.36s

1.     (Velocity after a period of time)

V_f  =  V_o + at

2.      (Distance after a period of time)

X_f = V_ot  + at²

3.     (Velocity/distance/acceleration without time)

V_f² =  V_o² + 2aDX

4.       (center seeking acceleration or centripetal acceleration)

A_c = V² / r

5.     (Work)

W =  D (mgh) +  D(1/2mV ²)

6.      (Change of momentum (Dr )=  Impulse)

D(mV) = D(f)(t)

7.      (Power with work)

P_avg =  W/t

8.      (Power with veolcity)

P = F(V)

9.      (Force exerted by a springy)

F_s = KX

10.  (Potential energy of a spring)

U_s = 1/2kx²

11.  (period of a spring)

T_s = 2p √ (m/k)

12.  (period of a pendulum)

T_p = 2p √ (L/g)    or    2√ L (on Earth)

13.   (relationship between period and frequency)

T = 1/f

14.  (Newton’s Law of Gravitation)

F_g = G (m₁m₂ ) / r²

15.  Pressure (with atmosphere) of a liquid

 P = p_o  + r g h

16.  (Force of buoyancy)

F_buoy =  weight of Liq displaced = mg = DVg

17.  (Equation of continuity for a liquid)

A₁V₁ =  A₂V₂

Free Resp #2 (Two Body Tension)   (2000B#2)

a. 4 forces:

• f & T up the plane (opposite direction  of motion)

• W down toward the Earth

• F_N Perpendicular (90⁰) up from the plane

b. SF = 0

             T + f = F_x  

                    f   =    F_x -  T

 m(Cos q)(m₁g)  = (Sin q)(m₁g)  - T

         m =  (Sin q)(m₁g) - T / (Cos q)(m₁g) 

    or       m =  Tan q - [T / (Cos q)(m₁g)]

c. SF = 0     T_M  = Mg

                   T_M  =  Mg = F_x1 + F_x2 - f  - 2f

                        Mg = (Sin q)(m₁g) + (Sin q)(m₂g) - 3f

               M = (Sin q)(m₁) + (Sin q)(m₂) - (3f /g)

             M = (Sin q)(m₁ + m₂)  - (3f /g)

d.  F_net = m₁a   =  F_x - f

               m₁a = (Sin q)(m₁g) - f

                  a = (Sin q)(g) - (f /m₁)