As a descending elevator approaches the correct floor, it slows to a stop with a constant acceleration of magnitude 1m/s*2. The elevator descends 4.5m while it is slowing. We want to find how many seconds the elevator takes to slow to a stop.
Which kinematic formula would be most useful to solve for the target unknown?

E) Δx = vt - 1/2at²

Explanation:

In order to decide which kinematic formula is most useful in finding the time taken for the elevator to stop, let's list out the relevant variables in this problem first.

Take the downwards direction to be negative and the upwards direction to be positive.

We want an equation that relates all four of these variables.

All of the equations given in the answer choices A-D have the initial velocity in them, v₀. Since we do not have this variable, the only answer choice with acceleration, displacement, final velocity, and time is the last equation.

We would use this equation with respect to the y-direction.

Therefore, answer choice (E) is the correct answer. It is the most useful kinematic formula to solve for the unknown variable t.

a small object of mass 3.66 g and charge -17.6 µc is suspended motionless above the ground when immersed in a uniform electric field perpendicular to the ground. what are the magnitude and direction of the electric field?

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west