(1) In order to reduce the influence of air resistance on the vibration of a simple pendulum, the pendulum ball should be an iron ball. The length of the cycloid is about 1m, and the maximum swing angle of the simple pendulum is about 5. The second set of experimental data should be selected to calculate the local gravity acceleration.

(2) According to the periodic formula of a simple pendulum, T=2πLg, T2=4π2Lg. According to mathematical knowledge, the slope k of T2-L image is 4π 2g, and the local gravity acceleration g = 4π 2k.

(3) If you forget to add the radius of the pendulum ball when measuring the pendulum length, the pendulum length becomes the length of the cycloid, and there is T2=4π2Lg=4π2(l line +r)g=4π2l line g+4π2rg. According to mathematical knowledge, the straight line G with T2=4π2l is parallel to the solid line T2 = 4 π 2l, and the straight line moves to the left.

So choose B.

So the answer is:

( 1)2.？

(2)4π2k

(3)B