Answer:C
Explanation:
Power=280watts=280/1000 kilowatts
Power=0.28 kilowatts
Device use 0.28 kilowatts in 1 day
1day=24hours
Device use 0.28 kilowatts in 24hours
30days=30 x 24=720 hours
For 720 hours=(0.28x720) ➗ 24
For 720 hours=201.6 ➗ 24
For 720 hours=8.4
Answer:
3.46 seconds
Explanation:
Since the ball is moving in circular motion thus centripetal force will be acting there along the rope.
The equation for the centripetal force is as follows -
Where,
is the mass of the ball,
is the speed and
is the radius of the circular path which will be equal to the length of the rope.
This centripetal force will be equal to the tension in the string and thus we can write,

and, 
Thus,
m/s.
Now, the total length of circular path = circumference of the circle
Thus, total path length = 2πr = 2 × 3.14 × 2 = 12.56 m
Time taken to complete one revolution =
=
= 3.46 seconds.
Thus, the mass will complete one revolution in 3.46 seconds.
Answer:
A) Out of the page.
Explanation:
Right-hand rule points the direction of the magnetic field at any point.
<u>Top wire</u>: Current is to the left. Point your thumb to the left and curl your other fingers around the wire. The tips of the four fingers points the direction of the field at that point. In this case, out of the page.
<u>Bottom wire</u>: Current is to the right. Point your thumb to the right and curl your other fingers around the wire. The tips of the four finger points out of the page again.
So, the total field produced by both wires is directed out of the page.
Another method to figure out the direction is the mathematical method.
Use the B-field formula:

The cross product between the direction of the current and the target position gives the direction of the B-field. If the left is -x direction and downwards is the -y direction, then
for the top wire.
for the bottom wire.
Answer:
E
Explanation:
Using Coulomb's law equation
Force of the charge = k qQ /d²
and E = F/ q
substitute for F
E = ( K Qq/ d² ) / q
q cancel q
E = KQ / d²
so twice the distance of the from the point charge will lead to the E ( electric field ) decrease by a 4 = E/4. E is inversely proportional to d²