Kinetic Energy $KE = \frac{1}{2}mv^2$. If the velocity is doubled ($2v$), the kinetic energy will increase 4 times ($KE' = \frac{1}{2}m(2v)^2 = 4 \times \frac{1}{2}mv^2 = 4KE$).

Physical quantities that have both magnitude and direction are called vector quantities, e.g., Force, Velocity, Acceleration.

A solar cell is a semiconductor device that converts solar light energy into electrical energy. This device is based on the photovoltaic effect.

According to Newton's third law of motion, action and reaction forces always act on two different bodies that interact with each other.

Since the forces are in opposite directions, the resultant force $= F_1 - F_2 = 5 N - 3 N = 2 N$.

Bats detect obstacles using ultrasonic waves.

Time period = Total time / Number of oscillations = 40/20 = 2 seconds.

According to Newton's first law of motion, if an object is in uniform motion (constant velocity), the net external force acting on it is zero. Since the table is frictionless, there is no resistive force, therefore no force is required.

Correct order (increasing capacity): R.A.P.S.-1 < T.A.P.S.-1 < N.A.P.S.-2 < K.K.N.P.P.-2.

When the lift is stationary or moving with uniform velocity, the acceleration inside the lift is $a = 0$. Therefore, the effective gravitational acceleration acting on the coin remains $g$ in both situations. Hence $t_1 = t_2$.

The standard unit of Work and Energy is Joule.

Distance 1: $18 \times \frac{10}{60} = 3 \, km$. Distance 2: $36 \times \frac{15}{60} = 9 \, km$. Total distance = $3 + 9 = 12 \, km$.

In physics, the measure of the earth's gravitational force on an object is called weight.

Diesel engines convert heat energy into mechanical energy, and solar cells convert light energy into electrical energy. Thus, (i) and (ii) are correctly matched.

The capacity to do work due to the state or position of an object is called potential energy. The energy stored in the watch spring is potential energy.

Inertia is directly proportional to mass. The object with the highest mass will have the highest inertia. Among the given objects, the truck has the highest mass.

According to Bohr's atomic model, electrons can only revolve in those orbits in which their angular momentum ($L$) is an integer multiple of $h/2 \pi$, i.e., $L = n(h/2 \pi)$.

A pendulum clock runs fast in winter because its periodic path and time period decrease.

The product of an object's mass ($m$) and velocity ($v$) is called momentum ($p = mv$).

Work done is equal to the change in kinetic energy. $W = \Delta K = \frac{1}{2} m (v_2^2 - v_1^2) = \frac{1}{2} \times 2000 \times (20^2 - 10^2) = 1000 \times (400 - 100) = 1000 \times 300 = 300,000 \, J = 300 \, kJ$.