Physics Answers

A motor cyclist travelling at 12m/s decelerates at 3m/s².

a) How long does it take?

b) how far does he travel in coming to rest?

Raindrops falling from thunderclouds may carry charges as high as 3.3*10-11 C/drop. According to The Rayleigh limit; what is the minimum size of drop

a stone is thrown horizontally from the roof of a building 15 m high with an initial speed of 5 m/s. How long will it take before the ball hits the ground?

A 50 kg tricycle travelling 6 m/s east and another tricycle with the same mass moving to the west at 3 m/s collided. Suppose the

collision did not damage any of the vehicles but caused the tricycles to move to the west at 3 m/s and to the east at 6 m/s, respectively.

Prove the law of conservation of momentum in this scenario.

The resistance of a copper wire increases by a factor of 1.62 when current flows through the wire compared to its resistance when no current flows and its temperature is 20o C. What is its temperature when the current flows?

A platinum resistance thermometer consists of a coil of 0.10-mm-diameter platinum wire wrapped in a coil. (a) What is the length of the wire needed so that the coil’s resistance at 20^o C is 25 Ω. The resistivity of platinum at this temperature is 1.0 x 10^-7 Ω.m. (b) What is the temperature of this platinum wire when its resistance increases 35% of its initial temperature? The temperature coefficient of resistivity for platinum is 3.92 x 10^-3 /^o C.

1. Two charges are 60cm apart, in air. One charge Q1 is +1.67 x 10^-7C; The other Q2 is

-1.67 x 10^-7 C. What is the electric field intensity at P midway between the charges?

2. The average distance between the electron and the proton in a certain atom is 5 x 10^-10m. How strong is the electric field that the proton experiences?

3. Two charges Q1 = 2.3 x 10-9C and Q2 = 3.5 x 10-9C, are 55mm apart. What is the electric field halfway between them?

4. Two charges of 6uC are 2.5m apart. Where is the electric field along the line joining them equal to zero?

5. What is the electric field at one vertex of an equilateral triangle whose sides are 10cm long if there are charges of -30uC at the other vertexes?

Explain: Can the force caused by an electric field be greater than the force due to a gravitational field? Give an example to prove this.

A magnetic field B= 0.6T is directed upward through a circular loop of diameter 7 cm and 500 turns. The loop is initially horizontal, so it is perpendicular to the magnetic field. It rotates through a horizontal axis so that the plane of the loop is at 74° with the horizontal axis within 1 second. What is the magnitude of the induced emf? 

6. A piece of aluminum with mass 1.00 kg and density 2 700 kg/m³ is suspended from a string and then completely immersed in a container of water. Calculate the tension in the string (a)

before and (b) after the metal is immersed.

3. A 950-kg cylindrical can buoy floats vertically in salt water. The diameter of the buoy is 0.900m. Calculate the additional distance the buoy will sink when a 70.0-kg man stands on top of it.