Answer:
Gravity,momentum & friction are examples of FORCE.
Explanation:
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The direction of magnetic field lines get reversed as the direction of magnetic field lines is from north pole to south pole
Answer:
d ≈ 320000 km
Explanation:
Echoes occurs as a result of the bouncing back of sound waves as it impinges on an obstacle. Since the echo covers two distances (i.e forth and back) the distance is written as 2d.
Velocity of radio waves is taken as the speed of light = 
time =2.15s
DISTANCE = VELOCITY *TIME
2d=vt


d= 322500000m
Distance to the moon is approximately 320000km
Given:
<em>Resistance = R </em>
<em>Lenght of second wire (L2)= half of the first wire's lenght (L1) = L1/2</em>
<em>Diameter of the second wire (D2)= Half of the first wire's diameter(D1) = D2/2</em>
Apply:

Where:
R= resistance
ρ= resitivity
L= lenght
A = cross sectional area
Replacing:
R = ρL2/A2
R= ρ (L1/2)/ (πd2^2 /4 )
R= 2ρL / π (d/2)^2
R= 2ρL / [πd^2/4]
R=2 ( 4ρL/πd^2)
R= 2R
Answer = 2R