The percentage and force of Friction ( 9/28/09)

[sumo87]

Homework Statement

Hi everyone,

I have 2 quick Questions, about my HW so if u think u can give me a hit please post.

Homework Equations

the Question was :-

10g bullet is fired into a ballistic pendulum made from a 4kg wood block and two light cords. The block's vertical displeacment is 5 cm.

1-

what is the inital velocity.

what percentage of the bullet's initial kinetic energy is lost in the collision

what is the force of friction acting on the bullet in the block assuming that it stops in 3 cm

The Attempt at a Solution

I found the initial velocity into the equation

1/2mv^2 = mgh

and i got 19.8 m/s

so please help me with 2nd and the 3rd Qs

 

[sumo87]

k i got for the 3ed Q

1.5E-3

I used the equation

F= ma

 

[tomcue]

Hello,

It seems like you are working on a problem involving a ballistic pendulum and the loss of energy and force of friction. It's great that you have already found the initial velocity of the bullet using the equation 1/2mv^2 = mgh. For the second question, you can use the conservation of energy principle to find the percentage of kinetic energy lost in the collision. This principle states that the total energy before the collision is equal to the total energy after the collision. Since the bullet and the block are the only objects involved in the collision, the initial kinetic energy of the bullet (1/2mv^2) will be equal to the final kinetic energy of the bullet and the block (1/2(m+M)V^2), where M is the mass of the block and V is the final velocity of the bullet and the block. You can solve for V using the equation 1/2mv^2 = 1/2(m+M)V^2 and then calculate the percentage of kinetic energy lost using the equation (initial kinetic energy - final kinetic energy)/initial kinetic energy * 100%.

For the third question, you can use the equation Ff = µN, where Ff is the force of friction, µ is the coefficient of friction, and N is the normal force. The normal force will be equal to the weight of the block and the bullet (mg + Mg), and you can calculate the coefficient of friction using the equation µ = Ff/N. Once you have found the coefficient of friction, you can use it in the equation Ff = µN to calculate the force of friction.

I hope this helps guide you in the right direction. Good luck with your homework!