The answer is B (The second one). I'm not sure though.
The spring constant is 4 N/m
Explanation:
When a spring is stretched/compressed by the application of a force, the relationship between the magnitude of the force applied and the elongation of the spring is given by Hooke's law:

where
F is the magnitude of the spring applied
k is the spring constant
x is the elongation of the spring, relative to its equilibrium position
For the spring in this problem, we have:
F = 0.12 N (force applied)
x = 3 cm = 0.03 m (elongation of the spring)
Therefore, we can solve the formula for k to find the spring constant:

Learn more about forces:
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To increase the acceleration of the car using the same engine, the mass of the car must be decreased.
<h3>
What is Newton's first law of motion</h3>
Newton's first law of motion states that an object at rest or uniform motion in a straight line will continue in that path unless acted upon by an external force.
The first law is also called the law of inertia because it depends on the mass of the object. The greater the mass, the greater the inertia and more reluctant the object will be to move.
Thus, to increase the acceleration of the car using the same engine, the mass of the car must be decreased.
a = F/m
Learn more about Newton's law here: brainly.com/question/25545050
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7.5 x 10⁻¹¹m. An electromagnetic wave of frecuency 4.0 x 10¹⁸Hz has a wavelength of 7.5 x 10⁻¹¹m.
Wavelength is the distance traveled by a periodic disturbance that propagates through a medium in a certain time interval. The wavelength, also known as the space period, is the inverse of the frequency. The wavelength is usually represented by the Greek letter λ.
λ = v/f. Where v is the speed of propagation of the wave, and "f" is the frequency.
An electromagnetic wave has a frecuency of 4.0 x 10 ¹⁸Hz and the speed of light is 3.0 x 10⁸ m/s. So:
λ = (3.0 x 10⁸ m/s)/(4.0 x 10¹⁸ Hz)
λ = 7.5 x 10⁻¹¹m
Explanation:
They will repel, meaning that they are made of an electrical conductor.