What metric unit would you use to estimate the actual distance between boston and new york?

The image shows a pendulum in simple harmonic motion the pendulum starts at a and swing to e

Which accurately compares concave and convex lenses?

Under the action of a constant force an object accelerates at 7.8 m/s2. what will the acceleration be if (a) the force is halved? (b) the object's mass is halved? (c) the force and the object's mass are both halved? (d) the force is halved and the object's mass is doubled?