8. A 20 newton object is pulled along a surface at a constant speed of 3.0 meters per second using a force of 4.5 newtons. The kinetic coefficient of friction is closest to (1) 0.23
(2) 0.30
(3) 0.67
(4) 4.4

Proof: Draw sketch / Show calculations.

Electric charge is uniformly distributed inside a nonconducting sphere of radius 0.30 m. the electric field at a point p, which is 0.50 m from the center of the sphere, is 15,000 n/c and is directed radially outward. what is the maximum magnitude of the electric field due to this sphere

Could someone . i have tried to solve myself but my calculation is off

(2) (a) you have a simple circuit that consists of only a battery (δvbat=1.5v) and two resistors with resistance r1=10ω and r2=5ω, connected in series with each other. what is the current running through the battery? (b) you re-arrange your circuit so now r2 is attached in parallel to r1 rather than in series. what is the current running through the battery? (c) you add an additional resistor r3=7ω on the same branch as r2. what is the current running through the battery? (d) what is the power dissipated in r3?