A 40 kg box is placed on a 2 m tall shelf. a. What is the gravitational potential energy of the box? b. If the box falls off the shelf, what is its kinetic energy as it strikes the ground? c. What is the velocity of the box immediately before it strikes the ground?

Answer:a) P. E = mgh

where m=40kg g=9.8m/s^2 h=2m

P. E=40*10*2

=800N

b) K. E=P. E

i. e, 1/2mv^2=mgh

1/2v^2=gh

where, g=9.8 h=2 v=?

1/2v^2=9.8*2

v^2=19.6*2

v^2=39.2

v=6.26m/s

therefore, K. E=1/2mv^

1/2*40*6.26^2

1/2*1567.5

K. E=783.8N

c) K. E=1/2mv^2

where, K. E=783.8N m=40kg v=?

783.8=1/2*40*v^2

783.8=20v^2

v^2=783.8/20

v^2=39.19

v=√39.19

v=6.26m/s^2