Science 8

3. It is done by a force which is a kind of
energy input that displaces an
object/move an object over a distance
parallel to the force applied.

4.  The SI unit of work is 1 N-m (newton-meter)
or 1 joule.
It is named after JAMES PRESCOTT JOULE (1818-
1889).
o A british physicist
o Showed the relationship of mechanical work and
energy

5. 1. if you lift a weight off the ground and then
place it back on the ground the distance (or
displacement) is zero.
2. pushing a heavy cart
3. Lifting a book from the table

6. work
force
distance/displacement

7. Sample problem:
1. A 10 kg object experiences a horizontal force which causes it to
accelerate at 5 m/s2, moving it a distance of 20 m, horizontally. How
much work is done by the force?
a. Identify the given:
Mass = 10 kg; accelearation= 5 m/s2; distance = 20 m
force=? And work=?
b. solution:
F=m x a = 10kg x 5 m/s2 = 50 kg. m/s2 or N
W = F x d = 50 N x 20 m
C. Answer: 1000 J

8. 2. A block is pulled by a constant force of 40 Newton. If the work done
by the force on the block is 680 joule what is the displacement of the
block?
a. Identify the given:
force = 40 N; work=680 J; distance = ?
b. solution:
d = W/F
d = 680 J x 40 N
C. Answer: 27, 200 m

9. Practice!
1. A block displacement cause of a force in a horizontal surface is 13
meter and the work done by the force on the block is 15.6 joule. Find
the magnitude of the force!
2. A boy lifts up a book from the floor to the table. The mass of the
book is 300 gram and the height of the table is 80 cm. (remember
that the distance should be on meter unit so centimeter should be
converted to meter)