As the phase difference between two interfering waves changes from 180° to 0°, the amplitude of the resultant wave A) Decreases
B) Increases
C) Remains the same

Your target variable is δf, the magnitude of the difference in frequency between the waves emitted from the sonar device and the waves received by the device after reflecting off the whale. write an expression for δf in terms of the relevant frequencies using the subscript notation introduced above.

When the force acting on an object points at least partially in the direction of the motion the work done is considered to be negative

Polly is pushing a box across the floor with a force of 30 n. the force of gravity is –8 n, and the normal force is 8 n. which value could describe the force of friction if polly could not move the box?