Wed 20 Oct:

Target: Understanding Torque (Review)

Journal:

Mr.  Brockhoff was riding down Whistler Mountain (see below) in the Extreme Games last summer. He Applied a 500,000 N force at a

60⁰ angle to the peddle. The peddle had an arm of .4 m.

What was the applied torque?              500,000N           

                                                                             60⁰                                                                        

Mr. Brockhoff jumping a 800m wide gorge.  

Torque:

Force times distance at a 90⁰ angle

t = 500,000N (.4m)(Sin 60⁰) = 173,205Nm

 

 

 

1. a. What is the speed of a "bob" on a pendulum if it falls .4m?    

 

 

 

                              h₁ = .4m

 

 

 

 

 

 

 

 

 

 

                                                                   h₂ = 1.2m

 

 

 

                                                                                                  x

 

 

 

b. If the bob is released at the bottom of the swing and it falls 1.2 m to the ground, then how long will it take for the bob to hit the floor?

 

 

c. How far will it move horizontally ?

 

 

 

 

 

 

 

 

a.   mgh = 1/2 mv²

        ^{(10)(.4) = 1/2} v²

       V = 2.8m/s

 

b. h₂ = V_ot + 1/2at²

 à -1.2 m = 0 + 1/2(-10m/s²)t²

 à -1.2 m/(-5 m/s²)  = t²

      t = .49s 

 

c.  x =  V_ot + 1/2at²   

 à x = (2.8 m/s)(.49s) + 0

           x = (2.8 m/s)(.49s)   = 1.4 m

 

 

 

 

                                                                                              (F₁)

                                                                                100N

 

 

                                         5m            2m       3m

 

 

 

 

             A                   (W)            B

                         50N

 

 

 

 

 

 

 

 

 

       CCWt = CWt

(F_B)(x) =   (W)(x_w) + (F₁)(x₁)

(F_B)(10m) = (50N)(5m) + (100N)(7m)

(F_B)(10m) = (250Nm) + (700Nm)

          F_B    =      95N

     F_A + F_B    =   150N

    F_A + 95N  =   150N 

           F_A   =   55-Nm

 

 

 

 

3. A pump lifted water up to a house 12m above the stream. If it was a 400W pump how much water did it move in 3 minutes.

Ans #2:

PE (mgh) per 1.0 kg

PE = (1kg)(10N/kg)(12m) = 120 J per kg

P=W/t  --> W = Pt      also    W = DPE

W =  (P)(t) = (400 J/s)(180s) =  72,000 J   (of PE)

72,000 J / 120 J per kg =  600 kg of water

3. a. What is the impulse experienced when

Jason (70 kg) lands on a hard ground after

jumping from a height of 5.0 m?

final V à V_f² – V_i² = 2aDx

       à V_f² – 0 = 2(-10)(-5)

       à V_f = √ 100 à -10m/s (going down)

a.  Impulse = D momentum

     Impulse =  mDV

     Impulse = 70{0 - (-10)} à 700 Ns     

Go over Test Ch 4-6