A person driving a car suddenly applies the brakes on seeing a child on the road ahead. If he is not wearing the seat belt, he falls forward and hits his head against the steering wheel. Why?

A woman throws an object of mass $500 \mathrm{g}$ with speed of $25 {\text{m s}}^{-1}$.

What is the impulse imparted to the objects?

A woman throws an object of mass $500 \mathrm{g}$ with speed of $25 {\text{m s}}^{-1}$.

If the object hits a wall and rebounds with half the original speed, what is the change in momentum of the object?

 A mass of$2 \mathrm{kg}$ is suspended with thread $AB$ (figure). Thread $CD$ of the same type is attached to the other end of $2 \mathrm{kg}$ mass. Lower thread is pulled gradually, harder and harder in the downward direction so as to apply force on $AB$. Which of the threads will break and why?