Battery based heaters use electric resistance heating, which uses a lot of current (electricity) to create the heat.
D. Gravitational potential
Answer:
E=3 x 10^4 N/c
Explanation:
The electric field strength can be found out disk with a uniform positive surface charge density by

σ= charge density
r= radius of the disk
z= position in which we have to find electric field = 15 cm
ε_0= constant ( vacuum permitivity)
putting values we get

solving we get
E=30000 N/c
E=3 x 10^4 N/c
The answer is C. Muscular strength is the force produced in a single maximum effort.
Answer : Radius of Earth is 6,340 Km.
Explanation
It is given that,
Tangential velocity of Earth at the equator, v = 465 m/s
Centripetal acceleration at the equation is, 
We know that the relation between centripetal acceleration and tangential velocity is :
..........(1)
Where,
v is tangential velocity
r is the radius
Putting all values in equation (1)


or

The Earth's radius is 6,340 Km. Hence, this is the required solution.