1. Copyright - Adam Randall Electrostatics – Practice Problems Problem 1 Problem 1 – Lunar Athletes & Apparent Weight Problem 1 Problem 2 Problem 2 – Electric Field Safety Net Problem 2 Problem 3 Problem 3 – Lunar Crater Jumping Problem 3 Problem 4 Problem 4 – Athlete’s Field Problem 4 Click on this icon to return to the this slide.

2. Copyright - Adam Randall B.Calculate the electric field (vector) needed to give an athlete an apparent weight equal to twice their weight on the Earth. A.If the athlete above wanted an apparent weight equal to their weight on the Earth, they would need this type of charge: Positive or Negative? In the future, many Olympic athletes will train on the moon because the moon’s gravitational force field is nearly 1/6 th of the Earth’s. Special training facilities will be built to maintain variable strength / uniform electric fields inside different rooms. Athletes will wear electrically charged body suits designed to evenly distribute electrical force. The result will be a unique training environment able to create apparent weights ranging from 1/6 th mg to 2mg. q = | 0.25 | C charge on athlete’s suit m = 72 kg athlete’s mass + +++++ ____________ Problem 1 Problem 1 Problem 1 Problem 1

3. Copyright - Adam Randall Problem 1 Problem 1 Problem 1 Problem 1 Answer 1 The electric field needed to produce an apparent weight equal to the athlete’s weight on Earth = 5174 N / C directed downward. + +++++ ____________

4. Copyright - Adam Randall Problem 2Problem 2Problem 2Problem 2 + ++ _ _ _ Photogate A. The net charge on the suit must be this to save the athlete: Positive or Negative. B. Predict the electric field needed in order to save the athlete by bringing them to rest on the floor. A 72 kg Lunar athlete falls from rest, 15 meters above the ground, wearing a body suit charged with |0.25 | C. As a built in safety measure a photogate placed 5.0 meters above the ground measures the speed of the falling athlete and turns on the electric force field safety net. The electric force field safety net is designed to decelerate an athlete in lunar freefall and bring them safely to rest on the surface of the floor. Coulomb’s Lunar Safety Net 5. 0 m 10. 0 m

5. Copyright - Adam Randall Problem 2Problem 2Problem 2Problem 2 + ++ _ _ _ Photogate Coulomb’s Lunar Safety Net Answers A.The athlete needs a net negative charge. B.The electric field needs to be = 1411 N/C downward in order to bring the athlete safely to rest on the floor.

6. Copyright - Adam Randall Consider a 120 kg athlete trying to jump the 125 kilometer wide lunar crater shown below. Their initial velocity is 4.5 m/s at 45 degrees. If the electric field points up and has a strength of 2.5x10 3 N/C, predict the minimum net charge the athlete must have on their body suit to jump the crater? Problem 3Problem 3Problem 3Problem 3

7. Copyright - Adam Randall Hint 3Hint 3Hint 3Hint 3 Decompose the initial velocity vector into components. Determine the total time in flight. Determine the vertical acceleration using ΔY= 0 meters. Use Newton’s 2 nd Law to find the charge on jumper. VoVo V oy V ox Hints

8. Copyright - Adam Randall The athlete must have at least + 7.8 x 10 -2 Coulombs of charge to make the 125 kilometer jump.

9. Copyright - Adam Randall Imagine four electrically charged athletes standing on the vertices of a square 2 meters on a side parallel to the surface of the moon. The two athletes on the top of the square carry -0.25 Coulombs of charge. The two athletes on the bottom of the square carry +0.25 Coulombs of charge. Proble m 4 A.Determine the electric field at the exact center of the square. B.Determine the electric force on a 0.1 gram water drop with 10,000 extra electrons on it, at the center of the square. C.Could you use the standard equations of kinematics to predict the motion of the water drop through space and time? 2 meters

10. Copyright - Adam Randall Answers Answer s 4 A. The Electric Field = 3.1 x 10 9 N/C Upwards. B.The Electric Force = 5.1 x 10 -6 N Downwards C.No! The force and therefore the acceleration changes with location. The electric field is non- uniform. 2 meters