# What is the % efficiency of this system ?

1. Jul 21, 2005

### PhysicsNoob88

These are some problems I am having difficulty with, the first problem I got an answer but I am unsure if it is correct and the others I have no clue. If you can step by step how to do them it would be greatly appericated.

A 12 kg. fish swimming at a velocity of 3 m/s swallows an absent-minded 4 kg fish swimming toward it at 10 m/s. What is the velocity, including direction (e.g., direction of larger fish or smaller fish), of the larger fish after lunch ?

I used m=mv and I got the answer to be -4m/s (big fish travels bacwards from its original postion) < I am not sure if this is correct if you can verify that would be awsome.

2) A pulley system is set up to lift boxes weighing 750 N from ground level to a position 6 meters high. A man pulls 30 meters of rope with a force of 200 N.

(b) If it takes the man 50 seconds to accomplish this task, (1) how much power is he putting in and (2) how much power is he getting out ?

(c) What is the % efficiency of this system ?

3) Consider the inelastic collision between two objects (A and B). Object A has a mass of 10 kg. and is moving at 12 m/s. Object B has a mass of 6 kg. and is moving at 8 m/s toward object A (Objects A and B are moving towards each other). How much energy is dissipated as heat ?

HINT: The velocity of the wreckage must first be determined. Then use the principle of conservation of energy.

To whom who ever does it I truely thank you.

Last edited: Jul 21, 2005
2. Jul 21, 2005

### PhysicsNoob88

I need the answers by 10 minutes from now, please anyone help...

3. Jul 21, 2005

### cscott

For number two, $P = \frac{W}{t}$ and $W= Fd$. Can you go from here?

4. Jul 21, 2005

the rules are that we don't do your homework for you.

5. Jul 21, 2005

### mukundpa

For No. 1 first conserve momentum and then v = momentum/mass

6. Jul 21, 2005

### mukundpa

For no.3
whether the collision is elastic or inelastic momentum is conserved.
The difference of initial and final energies is the heat dissipated.