Modern Physics
Questions & Answers
4. What are the strength and direction of an electric field that will balance the weight of a 1 g plastic sphere that has been charged to -3 nC?
Question 3 - Particle A of mass 130 kg is located at < 11, 13, 14 > m. Particle B of mass 320 kg is located at < 13, 17,6 > m.
1) State Hooke's law and write the equation for the spring system upto the limit of proportionality. 2) Write the mathematical relationship between Mass (in kg), Weight (in N) and acceleration due to gravity (g). 3) Sketch and label a graph of extension (AI) against Weight (W) including the limit of proportionality and beyond this point. 4) Show how you can work out the value of spring constant (k) from the graph.
A 0.50 kg pendulum bob is released from some initial height such that the speed of the bob at the bottom of the swing is 3.8 m/s. What is the initial height of the bob?
A spring is compressed by 0.044 m. What is the potential energy of the spring if the spring constant is 739 N/m. (an uncompressed spring has zero potential energy. Also, give your answer in joules to two decimal places)
A ball is held in place at one end of the spring as shown in the figure. The spring is initially compressed by 0.026 m and the released. When the spring reaches its relaxed (uncompressed) position, all of its potential energy is transferred to the ball's kinetic energy. What is the ball's kinetic energy at that instant if the spring constant is k = 277 N/m.
4) [Electric Potential Energy] A double-helix of DNA (deoxyribonucleic acid) acts like a spring and compresses upon becoming ionized and charged at the both ends. The double helix is 2.17μm long before charging, and compresses 1.5% after the DNA double helix becomes charged with negative charge of -3e at one end and a positive charge of +2e at the other end. For simplicity you may assume the DNA in vacuum. (a) What are the magnitude and direction of the electric field at the middle of the double helix in the compressed state? (b) What's the electric potential energy of the double helix when the compression just starts and after the compression completes? (c) If the compressed state is a mechanical equilibrium, what are the magnitude and direction of the elastic force at the two ends in the compressed state?
The pressure of residual gases in avaccum chamber at room temperature is 2.0x10-6 mbar (note: 1 mbar = 1 milibar = 10
7. a) What is the electric field at point P? b) An electron is placed at point P, what is the resulting force on the electron (magnitude and direction)? 6 nm q=-9pC
