# Impulse/Momentum QuestionWatch

#1
A bullet of mass 60g is fired into a 20kg block of wood which is suspended on a light inextensible wire to form a ballistic pendulum. After penetration the bullet remains in the wood. The vertical position of the wood-bullet combination increases by 28cm. Calculate the velocity of the bullet?

I know that you will have to use conservation of momentum here... However I am unsure of how i am going to do this with the given information. Ant tips? thanks
0
8 years ago
#2
(Original post by importunate)
...
One way to do it is to start from the end and work backwards.

You know the height the pendulum rose to, hence you can work out it's velocity just after impact, from energy considerations.

Then use conservation of momentum to find the velocity of the bullet.
#3
thanks. got it.
0
#4
Thanks for all of the help...

However I am going to be cheeky now and ask for some help on another questions.

A cork ball of mass 100g at rest is released from a height of 8.5m about the launch of a 100g dart which is projected vertically upwards with an initial velocity of 12m/s. Upon impact the cork and the dart stick together. Calculate the velocity immediately after the collision.

My first thoughts on this are. I have to work out when the two items collide. I have to work out the velocities of the items before the collisions. I would then be able to use conservation of moment to work out the final velocity? Idea ideas of how else I should go about this?
0
8 years ago
#5
(Original post by importunate)
Not off the top of my head.

Working out the time is quite easy if you use s=ut+1/2 at^2 for each, and realise that the sum of the distances is 8.5, and t will be the same for each.
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