Tuesday 2 Nov:

 Target: Hooks Law

Free Response Q

Target: Hooke's Law

Notes:

          F = kx

  Work = D Potential Energy :  

        U = ½ kx²

1. If you compress a spring 10.0cm in order to shoot a 100g ball directly up at 3.0m/s. Find:

a. The height of the ball will reach.

b. The spring constant.

c. The spring’s work.

a. V_f²  = V_i²   + 2aDx

V_f² –V_i² = 2aDx

0 – 3² = 2(-10)x

x = 9/20 à .45m

            b. PE_g = U_s

            mgh = ½kx²

       (.1)(10)(.45) = ½k(.1)²

            k = .45/ .005 à 90N/m

c.  U_s = ½ kx²

 U = ½(90) (.1)²

 U = .45J

Check answer to gravitational PE

PE = mgh à (.1)(10)(.45) = .45J

2) a) A 1.0kg mass lowers (stretches) a spring from the rest position a distance of 20cm. Find k

b) Then, a 6.0kg block replaces the 1.0kg block, and is released from the rest position . What is the displacement of the spring when the mass stops it descent?

Rest Position

Ending Pt

a) F = kx

10 = k(.2)

k = 50N/m

b) loss of PE of object = U_s

mgx = ½ kx²   (x are crossed out on both sides)

(6-kg)(10-N/kg) = ½ (50-N/m)(x)

60-N/(25-N/m)  = x

x = 2.4m

Lab: Mickey

Determine the k for the compressed  objects