The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be quickly changed by controlling the amount of electric current in the winding. However, unlike a permanent magnet that needs no power, an electromagnet requires a continuous supply of current to maintain the magnetic field.
Answer : The value of the constant for a second order reaction is, 
Explanation :
The expression used for second order kinetics is:
![kt=\frac{1}{[A_t]}-\frac{1}{[A_o]}](https://tex.z-dn.net/?f=kt%3D%5Cfrac%7B1%7D%7B%5BA_t%5D%7D-%5Cfrac%7B1%7D%7B%5BA_o%5D%7D)
where,
k = rate constant = ?
t = time = 17s
= final concentration = 0.0981 M
= initial concentration = 0.657 M
Now put all the given values in the above expression, we get:


Therefore, the value of the constant for a second order reaction is, 
Answer:
D. 2.5 Hz
Explanation:
Frequency = speed of wave / wavelength
= 335 /140 ( from graph)
= 2.4
Answer:
75.645 J
Explanation:
The kinetic energy is related to the mass and velocity by the formula ...
KE = 1/2mv²
For the given mass of 0.045 kg, and velocity of 41 m/s, the kinetic energy is ...
KE = 1/2(0.045 kg)(41 m/s)² = 75.645 J
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The unit of energy, joule, is a derived unit equal to 1 kg·m²/s².
Answer: a boy jumping down