10 points A very light ideal spring with a spring constant (force constant) of 250
N/m pulls horizontally on an 18-kg box that is resting on a horizontal floor.
The coefficient of static friction between the box and the floor is 0.65,
and the coefficient of kinetic friction is 0.45. What length is the spring
stretched just as the box is ready to move? *
o
0.46 m
0.32 m
0.25 m
0.21 m

e = 0.46 m

Explanation:

From the laws of friction, frictional force, F is proportional to normal reaction, R.

F₁ = μR

where μ is coefficient of friction; R = mg and g = 9.8 ms⁻²

Also, from Hooke's law, extension, e, in an elastic spring is proportional to applied force.

F₂ = Ke

where K is force constant of the spring

Since the box is just about to move, the coefficient of friction involved is static friction.

The force on the spring equals the frictional force experienced by the box the box; F₁ = F₂

Ke = μR

e = μR/K

where μ = 0.65; R = 18 kg * 9.8 ms⁻²; K = 250 N/m

e = (0.65 * 18 * 9.8)/250

e = 0.46 m

two charges are fixed in place on the x-axis as shown. the charge at x = 0 is negative and has magnitude q = 2 μcoulombs (1 μcoulomb = 10-6 coulombs). the charge at x = d, (d = +12 cm), is positive and has magnitude q = 4 μcoulombs. find a point x = xo along the x-axis at which the electric field is zero.

jupiter is the largest planet in our solar system, having a mass and radius that are respectively, 318 and 11.2 times that of earth. suppose that an object falls from rest near the surface of each planet and that the acceleration due to gravity remains constant during the fall. each object falls the same distance before striking the ground. determine the ratio of the time of fall on jupiter to that on earth.