Traditional Culture Encyclopedia - Photography and portraiture - (2011? Yancheng second model) Xiao Ming follows his father on the swing as shown in the picture. Assume that the length of the pendulum rope is 3m, and the hanging point is on the beam. The quality o

(2011? Yancheng second model) Xiao Ming follows his father on the swing as shown in the picture. Assume that the length of the pendulum rope is 3m, and the hanging point is on the beam. The quality o

(2011? Yancheng second model) Xiao Ming follows his father on the swing as shown in the picture. Assume that the length of the pendulum rope is 3m, and the hanging point is on the beam. The quality of Xiao Ming and the bottom plate is ***

(1) As shown in the figure, when the external force is perpendicular to the swing rope, it is smallest. Fmin=mgsin37°=360N

(2) Ep=-mglcos37°=-1440J

(3) Assume that during Xiao Ming’s first downward swing, the change in kinetic energy is △EK, the change in gravitational potential energy is △EGP

When Xiao Ming is at the lowest point, he obtains from Newton’s second law:

F?mg=mυ2l

The solution is υ=3m/s

After passing the lowest point, the kinetic energy of Xiao Ming and the bottom plate is EK=12mυ2=270J

The reduction in the gravitational potential energy of Xiao Ming and the bottom plate is △EGp=360J , then △EGP>△EK

It means that Xiao Ming’s mechanical energy decreases during the downward swing, and the maximum deflection angle of the swing to the other side for the first time is less than 37°.

Answer:

(1) The minimum external force exerted by Xiao Ming’s father is 360N;

(2) Take the zero potential energy reference plane at the hanging point, before letting go The gravitational potential energy of Xiao Ming and the bottom plate is -1440J;

(3) The maximum deflection angle of the swing to the other side for the first time is less than 37°.