Answer:

Explanation:
As per Ampere's law the magnetic field at the surface of the wire is given as

here we have

so we will have

now again we use same value of current but wire with double the diameter
so the magnetic field at the surface is given as

so we have

Answer: Torque T = 40.7 Nm
Explanation:
Torque or turning effect is the rotational equivalent of linear force, i.e moment of force about a point.
Given that the force is applied perpendicular to the edge (angle 90°)
Torque can be represented by T;
T = FrSin∅ = Fr ( sin90 = 1)
T = force × distance
T = F × r
F = 55N
r = 74cm = 0.74m
T = 55N × 0.74m
T = 40.7 Nm
First we will use the concepts of motion kinetics for which the final speed is defined as shown below,

Here,
= Final velocity
= Initial velocity
a = Acceleration
s = Distance
Replacing,


Using the conservation of energy for kinetic energy we have,



Therefore the kinetic energy of the car is 31900J
To solve this problem we will apply the concepts related to momentum and momentum on a body. Both are equivalent values but can be found through different expressions. The impulse is the product of the Force for time while the momentum is the product between the mass and the velocity. The result of these operations yields equivalent units.
PART A ) The Impulse can be calculcated as follows

Where,
F = Force
Change in time
Replacing,


PART B) At the same time the momentum follows the conservation of momentum where:
Initial momentum= Final momentum
And the change in momentum is equal to the Impulse, then

And

There is not initial momentum then



<span>3.92 m/s^2
Assuming that the local gravitational acceleration is 9.8 m/s^2, then the maximum acceleration that the truck can have is the coefficient of static friction multiplied by the local gravitational acceleration, so
0.4 * 9.8 m/s^2 = 3.92 m/s^2
If you want the more complicated answer, the normal force that the crate exerts is it's mass times the local gravitational acceleration, so
20.0 kg * 9.8 m/s^2 = 196 kg*m/s^2 = 196 N
Multiply by the coefficient of static friction, giving
196 N * 0.4 = 78.4 N
So we need to apply 78.4 N of force to start the crate moving. Let's divide by the crate's mass
78.4 N / 20.0 kg
= 78.4 kg*m/s^2 / 20.0 kg
= 3.92 m/s^2
And you get the same result.</span>