Two ice skaters, frank and mary, are initially facing each other and separated by 2000 m on a smooth frozen lake. mary begins skating towards frank at t = 0 s with an acceleration of 0.75 m/s^2. after she reaches a speed of 12 m/s, she continues skating at a constant 12 m/s. three seconds after mary begins to skate, frank starts skating. he accelerates at 1.1 m/s^2 for 9 s and then skates at a constant speed. a) when do the skaters pass each other? b) how far from mary’s starting position is the point at which the skaters pass each other?

a) 99.1 s

b) 1093.2 m

Explanation:

The equation for speed with constant acceleration is

V(t) = V0 + a * t

Mary starts accelerating with a speed of zero, so

V0 = 0

V(t) = a * t

To reach a speed of 12 m/s

t = V(t) / a

t = 12 / 0.75 = 16 s

The equation for position under constant acceleration is

X(t) = X0 + V0 * t + 1/2 * a * t^2

Mary's starting position is zero

X0 = 0

X(t) = 1/2 * a * t^2

X(16) = 1/2 * 0.75 * 16^2 = 96 m

Frank starts skating 3 seconds after Mary, and he accelerates at 1.1 m/s^2 for 9 s. He will stop accelerating at second 12 (9 + 3).

His position after accelerating will be:

X(12) = X0 + V0 * (t - 3) + 1/2 * a * (t - 3)^2

His initial position is 2000, and his initial speed is zero

x(12) = 2000 - 1/2 1.1 * (12 - 3)^2 = 1955.5 m

Shi speed will be

V(12) = -1.1 * (12 - 3) = -9.9 m/s

From there they will move at constant speed from these positions.  We can consider them as moving at constant speed starting at t0 = 16 and t0 = 12 respectively.

For Mary:

X(t) = X0 + V0 * (t - t0)

X(t) = 96 + 12 * (t - 16)

For Frank:

X(t) = 1955.5 - 9.9 * (t - 12)

Equating these two we can find the time when they meet:

96 + 12 * (t - 16) = 1955.5 - 9.9 * (t - 12)

96 + 12*t - 192 = 1955.5 - 9.9*t + 118.8

21.9*t = 2170.3

t = 2170.3 / 21.9 = 99.1 s

Replacing this time value on either equation we get the position:

X(99.1) = 96 + 12 * (99.1 - 16) = 1093.2 m

i guess it’s a and b

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia