Answer:
m = 4.29 kg
Explanation:
Given that,
Mass of the object, m = 2.8 kg
Stretching in the spring, x = 0.018 m
Frequency of vibration, f = 3 Hz
Let m is the mass of the object that is attached to the spring. When it is attached the gravitational force is balanced by the force on spring. It is given by :



k = 1524.44 N/m
Since, 


m = 4.29 kg
So, the mass that is attached to this spring is 4.29 kg. Hence, this is the required solution.
The storm would be at least 7 miles away cause light travels faster than sound and you can tell how many miles away a lightning bolt might have hit by how long it takes the thunder to strike<span />
Answer:
292.3254055 W/m²
469.26267 V/m

Explanation:
P = Power of bulb = 90 W
d = Diameter of bulb = 7 cm
r = Radius = 
= Permittivity of free space = 
c = Speed of light = 
The intensity is given by

5% of this energy goes to the visible light so the intensity is

The visible light intensity at the surface of the bulb is 292.3254055 W/m²
Energy density of the wave is

Energy density is also given by

The amplitude of the electric field at this surface is 469.26267 V/m
Amplitude of a magnetic field is given by

The amplitude of the magnetic field at this surface is 
Answer:

Explanation:
The initial velocity, u, of the car=15m/s
The final velocity, v, of the car =0m/s
Time, t, taken for the car to come to a stop=5s
Acceleration is calculated by,

By substitution,



The negative sign implies that the car has decelerated.