Question

In a ballistics test, a 28-g bullet pierces a sand bag that is thick. If the initial bullet velocity was and it emerged from the sandbag moving at what was the magnitude of the friction force (assuming it to be constant) that the bullet experienced while it traveled through the bag?
A. 130 N
B. 1.3 N
C. 1.4 N
D. 38 N
E. 13 N

Answer 1

Answer:

A) 130N

Explanation:

We know that:

$E_i -E_f = W_f$

where $E_i$ is the initial energy, $E_f$ is the final energy and $W_f$ is the work of the friction force.

so:

$\frac{1}{2}MV_i^2 -\frac{1}{2}MV_f^2 = Fd$

where M is the mass, $V_i$ is the initial velocity,  $V_f$ is the final velocity, F the force and d the distance.

Replacing values, we get:

$\frac{1}{2}(0.028)(55m/s)^2 -\frac{1}{2}(0.028)(18m/s)^2 = F(0.3m)$

solving for F:

F= 126N

the closest answer is A. 130 N