Question

A bullet of mass $0.02{\text{ kg}}$ is fired from a rifle. The bullet takes $0.02{\text{ s}}$ to move through the barrel and leaves with a velocity of $200{\text{ m}}{{\text{s}}^{ - 1}}$ . What is the acceleration acting on the bullet?

Answer 1

Hint: Use the formula of force we have learned and try to imagine the situation which has occurred. Remember that at the beginning when the bullet was going to be fired, its velocity was $0{\text{ m}}{{\text{s}}^{ - 1}}$ , and at the end it is $200{\text{ m}}{{\text{s}}^{ - 1}}$ . Thus this is a simple problem of acceleration where initial and final velocities are given.

Complete step by step answer:
To find the value of acceleration, we need three variables, the initial velocity, the final velocity and the time and in the problem we can find each of the variables. By using the first equation of motion:
$v = {\text{ u + at}}$,
where $v$ = final velocity = $200{\text{ m}}{{\text{s}}^{ - 1}}$ ; $u$= initial velocity = $0{\text{ m}}{{\text{s}}^{ - 1}}$; $a$ = acceleration and $t$ = time = $0.02{\text{ s}}$ .
We can find the value of acceleration . From the formula , acceleration $a$= $\dfrac{{v - u}}{t}$.
$a$ = $\dfrac{{200 - 0}}{{0.02}}$
$\therefore a$= $10000{\text{ m}}/{{\text{s}}^2}$

Hence the acceleration of the bullet is $10000{\text{ m}}/{{\text{s}}^2}$.

Additional information: These questions can also be given by telling that $a$ is negative and that the bullet has stopped after travelling a said distance. We are to solve these questions by considering;
-The bullet travels in a straight line.
-There is no rebounce of the bullet after striking the target.
-Consider $v$ = Zero, as the bullet stops after travelling the said distance.
-The distance is calculated by multiplying average speed with time.

Note: These types of sums always use the same formula of the first equation of motion and only the data can be a bit interpreted. Always note that if the value of acceleration is negative then it is deceleration or acceleration in the direction opposite that of force applied. There can also be a sum of a bullet being struck in a wooden piece and a time will be given, where we need to find the acceleration of the bullet.