A contact lens is made of plastic with an index of refraction of 1.30. The lens has an outer radius of curvature of +1.96 cm and an inner radius of curvature of +2.56 cm. What is the focal length of the lens?
___cm

A block of mass m = 2.00 kg is released from rest at h = 0.600 m above the surface of a table, at the top of a ? = 40.0

A projectile is launched at an angle of 30 degrees above the horizontal at a speed of 300 m/s. In what direction is it traveling after 3 s? In other words, what is the direction of its velocity vector? (Use |g| = 10 m/s2.)

A 39 g block of ice is cooled to −67◦C. It is added to 518 g of water in an 64 g copper calorimeter at a temperature of 28◦C.

Find the final temperature. The specific heat of copper is 387 J/kg ·◦C and of ice is 2090 J/kg ·◦C . The latent heat of fusion of water is 3.33 × 105 J/kg and its specific heat is4186J/kg·◦C.

Answer in units of ◦C.

A 11.7kg weather rocket generates a thrust of 200N . The rocket, pointing upward, is clamped to the top of a vertical spring. The bottom of the spring, whose spring constant is 550N/m , is anchored to the ground.

A) Initially, before the engine is ignited, the rocket sits at rest on top of the spring. How much is the spring compressed?

B)After the engine is ignited, what is the rocket's speed when the spring has stretched 32.0cm ?

C)For comparison, what would be the rocket's speed after traveling this distance if it weren't attached to the spring?

A stick is resting on a concrete step with 1/7 of its length hanging over the edge. A single ladybug lands on the end of the stick hanging over the edge, and the stick begins to tip. A moment later, a second, identical ladybug lands on the other end of the stick, which results in the stick coming momentarily to rest 46.5° from the horizontal. If the mass of each bug is 3.43 times the mass of the stick and the stick is 16.3 cm long, what is the magnitude of the angular acceleration of the stick at the instant shown?

In a game of basketball, a forward makes a bounce pass to the center. The ball is thrown with an initial speed of 4.9 m/s at an angle of 20 ∘   above the horizontal. It is released 0.80 m above the floor.

What horizontal distance does the ball cover before bouncing?

Describe the differences between circular motions and elliptical motions. Explain how Newton’s universal gravitational law can be applied to study the interplanetary motions.

A proton is trapped in an infinitely deep square well of width L = 5 × 10^-6 nm. This is approximately the size of an atomic nucleus. (It depends on atomic weight.) The proton's mc² = 9.3827 × 10⁸ eV. Note: Atomic nuclei are really spheres. For simplicity, we are treating them as 1-D square wells, which yields the correct order of magnitude result.

1) What is the ground state energy of the proton in this well in eV? E₁ =

2) If the proton is in an excited state, it can fall to a lower energy state and emit a photon (just like an electron does). Suppose the photon's energy is 4.0959 × 10⁷ eV.

Note: This photon is a gamma ray, common in nuclear transitions. What was the proton's initial energy level (i.e., the n value)? n =

3) Suppose an electron were trapped in this well (infinitely deep, with the same width, L). What is the electron's ground state energy in this well in eV? E₁ =

A 6.000 g bullet Is fired with a velocity of 600.0 m/s towards a 2.000 kg stationary target. The target has frictionless wheels and rest on a horizontal surface. When the bullet hits the target, it becomes lodged in it, and the target and bullet move forward at a common velocity. Find the velocity of the bullet and target combination after the collision.

Block A (0.40 kg) and block B (0.30 kg) are on a frictionless table. Spring 1 connects block A to a frictionless peg at 0 and spring 2 connects block A and block B. When the blocks are in uniform circular motion about 0, the springs have lengths of 0.60 m and 0.40 m, as shown. The springs are ideal and massless, and the linear speed of block B is 2.0 m/s. If the spring constant of spring 1 is equal to 30 N/m, the unstretched length of spring 1 is closest to?

For example, Einstein postulated that the speed of light, c, is constant in all inertial frames of reference.

Bohr postulated that electrons go around the atom in orbits and that there are pre-defined orbits, and that moving from a higher orbit to a lower orbit makes releases energy.

I bet there are many other postulates that we take for granted.

Therefore I've a question, how can we claim something violates some physical law, when so many physical laws have been postulated?

All it takes is to disprove one of the postulates and suddenly a lot of things break down because of the claims that are based on the postulates.