A pile driver of mass 1000 kg falls freely through 3 m onto a post and drives the post 10 mm into the ground. Taking g = 10 m/s^2, what is the kinetic energy of the pile driver at the moment it strikes the post?
- 30 kJ.
- 45 kJ.
- 90 kJ.
Explanation from PART66Online
Falling 3 m, the pile driver converts its potential energy into kinetic energy: KE = mgh = 1000 x 10 x 3 = 30,000 J = 30 kJ at impact. KE = 1/2 mv^2 gives the same result: the impact speed satisfies v^2 = 2gh = 2 x 10 x 3 = 60 m^2/s^2, so KE = 0.5 x 1000 x 60 = 30,000 J. The 10 mm the post moves sets the average impact force (30,000 J / 0.01 m = 3 MN), not the kinetic energy on arrival.
R
ranz130 asked · 18 Aug 2013
still not get it,can somebody explain it.
Community Comments (4)
B
binoybose11
20 Aug 2013
i think its like this KE=PE
therefore 1/2mv2=mgh
mv2=2mgh
v2=gh
v2=10*3
v2=60
now, ke=1/2mv2
ke=1/2 1000*60
=1000*30
=30,000J
=30KJ
therefore 1/2mv2=mgh
mv2=2mgh
v2=gh
v2=10*3
v2=60
now, ke=1/2mv2
ke=1/2 1000*60
=1000*30
=30,000J
=30KJ
R
ranz130
20 Aug 2013
thanks..
J
Jacktrigg
24 Aug 2013
I think it wants you to calculate the potential
M
minnesota
20 Dec 2015
tnx
Please Sign In to post a comment.
More discussions in 2. Physics
- What work is done if a force of 100 N moves a body 15 metres?
- A good refrigerant has a
- The point at which an applied force overcomes friction and an object begins to move is the co-efficient of
- A mass of 20kg produces a momentum of 300kgm/s. What is the Kinetic energy?
- A mass of 20kg produces a momentum of 300kgm/s. What is the Kinetic energy?
- 1kg of water is heated from 0 degrees C to 2 degrees C. Its volume will