Answer:
true. b, c and d
Explanation:
Let's review each statement separately
a) False. The kinematics studies the position, speed and acceleration of the bodies, but not what causes these changes
b) True. Velocity is the displacement between time, displacement is a vector, and time is a scalar, so the division between them gives a vector
c) True. speed is the displacement that is a length between time, so its unit is length / time
d) true desaceleration = - aceleration
Answer:
F = 7.143 kN
Explanation:
given,
time taken to apply break = 1.05 s
car slows down from 15 m/s to 9 m/s
mass of the car = 1250 Kg
force is equal to the change in momentum with respect to time.
F = -7142.85 N
F = - 7.143 kN
Force is acting opposite direction of velocity of car i.e. the sign is negative.
Magnets attract when a north pole is introduced to a south pole. If like poles are introduced, either north to north or south to south, the magnets repel.
The main difference between mechanical and electromagnetic waves is that mechanical waves require a medium in order to propagate, while electromagnetic waves can propagate also in vacuum.
Examples of telecommunication via mechanical waves are sound waves (so, two people speaking to each other, for instance), while examples of telecommunication via electromagnetic waves are the radio waves that transmit the TV signals to the houses.
The H field is in units of amps/meter. It is sometimes called the auxiliary field. It describes the strength (or intensity) of a magnetic field. The B field is the magnetic flux density. It tells us how dense the field is. If you think about a magnetic field as a collection of magnetic field lines, the B field tells us how closely they are spaced together. These lines (flux linkages) are measured in a unit called a Weber (Wb). This is the analog to the electric charge, the Coulomb. Just like electric flux density (the D field, given by D=εE) is Coulombs/m², The B field is given by Wb/m², or Tesla. The B field is defined to be μH, in a similar way the D field is defined. Thus B is material dependent. If you expose a piece of iron (large μ) to an H field, the magnetic moments (atoms) inside will align in the field and amplify it. This is why we use iron cores in electromagnets and transformers.
So if you need to measure how much flux goes through a loop, you need the flux density times the area of the loop Φ=BA. The units work out like
Φ=[Wb/m²][m²]=[Wb], which is really just the amount of flux. The H field alone can't tell you this because without μ, we don't know the "number of field" lines that were caused in the material (even in vacuum) by that H field. And the flux cares about the number of lines, not the field intensity.
I'm way into magnetic fields, my PhD research is in this area so I could go on forever. I have included a picture that also shows M, the magnetization of a material along with H and B. M is like the polarization vector, P, of dielectric materials. If you need more info let me know but I'll leave you alone for now!