Answer:

Explanation:
1. Find the equation of eht maximal friction force:
The maximal friction force is given by the equation
, where μs is the static friction coefficient, m is the car´s mass and g is the gravitational force.
2. Replace values in the equation to find the answer:


Lines of Force around an Electromagnet. ... The magnetic field strength of an electromagnet is therefore determined by the ampere turns of the coil with the more turns of wire in the coil the greater will be the strength of the magnetic field.
Answer:
mu = 0.56
Explanation:
The friction force is calculated by taking into account the deceleration of the car in 25m. This can be calculated by using the following formula:

v: final speed = 0m/s (the car stops)
v_o: initial speed in the interval of interest = 60km/h
= 60(1000m)/(3600s) = 16.66m/s
x: distance = 25m
BY doing a the subject of the formula and replace the values of v, v_o and x you obtain:

with this value of a you calculate the friction force that makes this deceleration over the car. By using the Newton second's Law you obtain:

Furthermore, you use the relation between the friction force and the friction coefficient:

hence, the friction coefficient is 0.56
Work = (force) x (distance)
The worker does (40N) x (4m) = 160 joules of work.
Friction eats up (27N) x (4m) = 108 joules of that energy,
generating 108 joules of heat.
The remaining (160J - 108J) = 52 joules of energy moves the box.