1. Oct 16, 2008

### dsptl

* A system of blocks is released from the rest. the speed of 10kg block just before it hits the ground the ground. The surface is frictionless.

Attempt:

I hv donw this way, but I am suppose to use work-kinetic enery theoreom or something to find the answer, which i hv no clue abt it.........thought u guys would help me

first i found acceleration: a = g(M -m1sin45 - m2sin45)/(M+m1+m2) = 4.31 m2/s2

then used vf2 = vi2 +2ax = 0 + 2(4.31)(5) = 42.23m2/s2

and vf = 6.5m/s

2. Oct 16, 2008

### Redbelly98

Staff Emeritus

Use conservation of energy. Write an expression for the total energy just before things start moving. Then write an expression for the total energy when the block hits the ground.

3. Oct 16, 2008

### dsptl

our professor slightly went over it............can u please just write the expression, I can work tht out

Thanks a lot for helping

4. Oct 16, 2008

### Redbelly98

Staff Emeritus

The exact equations should be in your text book. There is (gravitational) potential energy and kinetic energy to account for.

5. Oct 16, 2008

### dsptl

but there r 3 blocks how do i add them together for the energy?

starting: (m1+m2+m3)gh = .5(m1+m2+m3)v*v

but I the height is not given for all the blocks......

6. Oct 17, 2008

### Redbelly98

Staff Emeritus

There are two problems here.

1. The heights are all different. So you'll have to use h1, h2, and h3 for the heights of each block. Don't worry that the heights are not all given, it will work out in the end.

2. Potential and kinetic energies are not equal to each other. Instead, you add them together, to find the total energy of the 3 blocks.

7. Oct 17, 2008