Name the unbalanced force which slows down a moving bicycle when we stop pedalling it.

Two balls $A$ and $B$ of masses $m$ and $2m$ are in motion with velocities $2V$ and $V$ respectively. Compare:
$(i)$ their inertia,
$(ii)$ their momentum,and
$(iii)$ the force needed to stop them in the same time.

Find the ratio of momentum of the two bodies $A$ and $B$ of masses $m$ and $4m$ respectively,moving with the same velocity $v$.

State Newton's third law of motion. Give two examples.

$(a)$ Define force and state three possible effects of force on an object.
$(b)$ $A$ motorcycle is moving with a velocity of $90 \, km \, h^{-1}$ and it takes $5 \, s$ to stop after the brakes are applied. Calculate the force exerted by the brakes on the motorcycle if its mass along with the rider is $200 \, kg$.

Give an example to show that friction is an important factor in satisfying Newton's third law of motion.