# Homework Help: I need help with my mechanical principles home work.

1. Jul 16, 2010

### james9.81

A drop hammer of mass 200kg falls freely through a distance of 2m to strike a forging and is brought to rest after a distance of 50 mm. The hammer does not rebound after impact. The mass of the forging is 500 kg. Determine the average resistance of the metal.

please can anyone solve this question, will be much appreciate :)

2. Jul 16, 2010

### Gear.0

I'm assuming by "resistance of the metal" they are asking you to either find the force applied on the hammer or the acceleration.

Break the problem into 2 parts. One is a simple free falling body problem, the other is the forging stopping the hammer (which is basically the free falling body in reverse with a different acceleration).

All you really care about is the second part, but you will need to gather information from the first part. So first, just think how you would solve the second part by itself, that should tell you what information you are missing. Then you will know what information you will need to solve for using the first part.

3. Jul 16, 2010

### james9.81

Therefore should i workout the velocity of the metal immediately after impact using the principle of conservation of momentum.

momentum of system before impact = momentum of system after impact

m1 V1 = (m1 + m2)v2
so v2 =m1 v1 / (m1 + m2) =

4. Jul 16, 2010

### Gear.0

I'm sorry, what exactly is a "forging"? and in what way does it stop the hammer?

5. Jul 16, 2010

### james9.81

forging is the shaping of metal, for example a blacksmith forges steel swords.The forging doesnt stop the hammer doesnt stop the hammer in anyway.

6. Jul 16, 2010

### Staff: Mentor

Hint: Consider the work done on the hammer as it is brought to rest. Use that to figure out the average force that the metal exerts on the hammer.

7. Jul 16, 2010

### james9.81

Thanks for the hint, helped alot

8. Jul 16, 2010

### Gear.0

I think he solved the problem, so I hope you won't mind if I ask something again.

You said the forging doesn't stop the hammer at all.. but then how does the hammer stop after 50mm ?