Pardon me for my stubborn classical/semiclassical brain. But I bet I am not the only one finding such description confusing.

If EM force is caused by the exchange of photons, does that mean only when there are photons exchanged shall there be a force? To my knowledge, once charged particles are placed, the electromagnetic force is always there, uninterruptedly. According to such logic, there has to be a stream of infinite photons to build EM force, and there has to be no interval between one "exchange event" to another. A free light source from an EM field? The scenario is really hard to imagine.

For nuclei the scenario becomes even odder. The strong interaction between protons is caused by the exchange of massive pions. It sounds like the protons toss a stream of balls to one another to build an attractive force - and the balls should come from nothing.

Please correct me if I am wrong: the excitations of photons and pions all come from nothing. So there should be EM force and strong force everywhere, no matter what type of particles out there. Say, even electrical neutral, dipole-free particles can build EM force in-between. And I find no reason such exchanges of particles cannot happen in vacuum.

Hope there will be some decent firmware to refresh my classical brain with newer field language codes.

A block of mass m1 = 2.9 kg initially moving to the right with a speed of 4.3 m/s on a frictionless, horizontal track collides with a spring attached to a second block of mass m2 = 5 kg initially moving to the left with a speed of 2.8 m/s as shown in figure (a). The spring constant is 572 N/m.

What if m1 is initially moving at 2.2 m/s while m2 is initially at rest?

(a) Find the maximum spring compression in this case. x = m

(b) What will be the individual velocities of the two masses (v₁ and v₂) after the spring extended fully again? (That is, when the two masses separate from each other after the collision is complete.)

Two boxes (m1 = 70.0kg and m2 = 51.0kg ) are connected by a light string that passes over a light, frictionless pulley. One box rests on a frictionless ramp that rises at 30.0? above the horizontal (see the figure below), and the system is released from rest. Find the acceleration of each box.

In a quarter-mile drag race, two cars start simultaneously from rest, and each accelerates at a constant rate until it either reaches its maximum speed or crosses the finish line. Car A has an acceleration of 10.9 m/s2 and a maximum speed of 109 m/s. Car B has an acceleration of 11.8 m/s2 and a maximum speed of 93.7 m/s. (a) Which car wins the race? (b) By how many seconds does this car win the race?

A 3.71 kg ball of clay is traveling straight north with a speed of 24.8 m/s, collides with a 3.65 kg ball of clay travelling strait east with a speed of 23.4 m/s. What is the speed of this new ball of clay after its collision? (I got 17.1 m/s) What direction is it traveling, given as a degree north of east?

A person with axial hypermetropia has a lens-retina distance of 1.9 cm and the maximum optical power of their eye is the same as that for a normal person.

A) what is the near point for this person?

B) What is the range accommodation this person needs to see objects from their near point all the way to their far point (Which is the same as for a normal eye)?

C) What is the optical power of the contact lenses used to treat this person and give them a normal near point of 25 cm>

A steel ball of mass 0.920 kg is fastened to a cord that is 34.0 cm long and fixed at the far end. The ball is then released when the cord is horizontal, as shown in the figure. At the bottom of its path, the ball strikes a 2.10 kg steel block initially at rest on a frictionless surface. The collision is elastic. Find (a) the speed of the ball and (b) the speed of the block, both just after the collision.

Why are diffraction gratings used to measure wavelength of light instead of double slits?

An electron is accelerated inside a parallel plate capacitor. The electron leaves the negative plate with a negligible initial velocity and then after the acceleration it hits the positive plate with a final velocity β. The distance between the plates is 14.2 cm, and the voltage difference is 146 kV. Determine the final velocity β of the electron using classical mechanics. (The rest mass of the electron is 9.11×10^-31 kg, the rest energy of the electron is 511 keV.)
7.559×10^-1

What is the final velocity β of the electron if you use relativistic mechanics?

3)When a power source like a battery is connected to a circuit, an electric field pushes electrons within the conducting wires causing them to flow. The electric field exists due to an uneven build up of charge on the surfaces of the wires (called a surface charge gradient). In this set of problems we will explore a simple model of how this all comes about and emphasize the connection between source charges, electric fields, and voltage differences in the context of electric circuits.

A very small segment of the conducting wire in a circuit can be modeled as a circular ring of radius 1 mm. Consider two such rings surrounding the z-axis separated by a small distance 2 mm. Let's first suppose that both rings have the same charge density. What is the strength of the electric field on the z-axis at the midpoint between the two rings?

4)If you used a voltmeter to measure the voltage difference between the centers of the two rings, what measurement would you read?

3) A soccer ball is kicked with an initial horizontal speed of 8 m/s and an initial vertical speed of 6

m/s. Identify the following quantities and include one short sentence to explain your answer using

the concepts of projectile motion (no calculations are necessary). Assume that projection and

landing height are the same and neglecting air resistance (4 pts):

a) The ball’s horizontal speed 0.5 seconds into its flight is:

because:

b) The ball’s horizontal speed midway through its flight is:

because:

c) The ball’s horizontal speed immediately before contact with the ground is:

because:

d) The ball’s vertical displacement up is (circle one) greater than/less than/the same as the

vertical displacement down because:

e) The ball’s vertical velocity halfway through its flight is:

because:

f) The ball’s vertical speed immediately before contact with the ground is:

because:

***answer in significant digits

A wheel with a weight of 395 N comes off a moving truck and rolls without slipping along a highway. At the bottom of a hill it is rotating at an angular velocity of 22.2 rad/s . The radius of the wheel is 0.647 m and its moment of inertia about its rotation axis is 0.800 MR2. Friction does work on the wheel as it rolls up the hill to a stop, at a height of h above the bottom of the hill; this work has a magnitude of 3524 J . Calculate h. Use 9.81 m/s2 for the acceleration due to gravity.

Consider a spacecraft in an elliptical orbit around the earth. At the low point, or perigee, of its orbit, it is 300km above the earth's surface; at the high point, or apogee, it is 2500km above the earth's surface.

A) What is the period of the spacecraft's orbit?

B) Using conservation of angular momentum, find the ratio of the spacecraft's speed at perigee to its speed at apogee.

C) Using conservation of energy, find the speed at perigee and the speed at apogee.

Enter your answers numerically separated by a comma.

D) It is necessary to have the spacecraft escape from the earth completely. If the spacecraft's rockets are fired at perigee, by how much would the speed have to be increased to achieve this?

E) What if the rockets were fired at apogee?

Two converging lenses with focal lengths of 40 cmand 20 cm are 10 cm apart. A 2.0 cm -tall object is 15 cm in front of the 40 cm -focal-length lens.

Calculate the image position and image height.

Please show work, thanks-