Pile driver question kinetic energy and potential energy

[dansbr]

1. a pile driver of mass 250kg is allowed to fall from rest through a distance of 2m on to a 400kg steel pile to drive it into the ground. Each impact drives the pile into the ground by 150mm. assuming that the pile driver remains in contact with the pile after impact and that momentum is conserved, calculate

the kinetic energy of the driver and pile after impact
the change in potential energy of the driver and pile combination on moving into the ground.



2. ke=0.5mv^2
pe=mgh


3. for the first one i thought that you should add the kinetic energy of the pile driver and pile, but wouldn't the velocity be 0 after impact.

for the second question would you calculate the PE of the pile and driver before impact and after impact and it would be the difference of the two.

can someone tell me if am correct

 

[tiny-tim]

hi dansbr!

calculate

the kinetic energy of the driver and pile after impact
…
3. for the first one i thought that you should add the kinetic energy of the pile driver and pile, but wouldn't the velocity be 0 after impact.

no, the question means immediately after impact

(it's a perfectly inelastic collision, so a lot of energy is lost on the impact)

for the second question would you calculate the PE of the pile and driver before impact and after impact and it would be the difference of the two.

not before and after impact, but before impact and after stopping