(i) Oscillatory motion

While running, the hands move to and fro and repeat their motion after a given interval of time. Hence, it is an oscillatory motion.

(ii)Straight line

The horse is pulling a cart on a straight road. Therefore, it has a motion along a straight line.

(iii)Circular motion

Merry-go-round has a circular motion. Therefore, a child sitting inside it will also have a circular motion.

(iv) Oscillatory motion

The child on a see-saw goes up and down continuously. It oscillates up-down. Therefore, it is an oscillatory motion.

(v)Oscillatory motion

The hammer hits the electric bell and vibrates rapidly. Therefore, it is an oscillatory motion.

(vi) Straight line

The train is moving on a straight bridge. Therefore, it has a motion along a straight line.

(i) Correct

Second is the SI unit of time.

(ii) Not correct

An object can move with constant or variable speed.

(iii) Correct

The distance between two cities can be very large. Since kilometre is a bigger unit of distance, the distance between two cities is measured in kilometres.

(iv) Not correct

Time period of a pendulum depends on the length of the thread. Hence, it is constant for a particular pendulum.

(v) Not correct

The speed of a train is measured either in km/h or in m/s.

Number of oscillations = 20

Total time taken to complete 20 oscillations = 32 s

$\mathrm{Time} \mathrm{period} = \frac{\mathrm{Total} \mathrm{time} \mathrm{taken}}{\mathrm{Number} \mathrm{of} \mathrm{oscillations}} = \frac{32}{20} =1.6 \mathrm{s}$

Distance between the two stations = 240 km

Time taken = 4 h

$\mathrm{Speed} = \frac{\mathrm{Distance}}{\mathrm{Time} \mathrm{taken}} = \frac{240}{4} =60 \mathrm{km}/\mathrm{h}$