Take a moment to understand this apparatus: Current passes through a rigid copper conductor mounted to a wood plate. The wood plate is mounted on a scale which measures the downward force exerted on the conductor. The scale is adjusted to read zero when no current flows. A magnet is placed next to the conductor, on a stand that is separate from the scale. When current flows through the conductor, the the interaction with the magnetic field causes a downward force on the conductor, which we can read on the scale. Which force is measured by the scale

explanation:

v=uf/(u-f)

= 5.-10/(5+10) convex lens has negative focal length

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.