Lesson 3.1 Homework Solutions
1.
Vector
A
= 2
i
– 3
j
and vector
B
= 4
i
+ 6
j
. Find
A
⋅
B
and the angle
between the two vectors.
A
= 2
i
– 3
j
,
B
= 4
i
+ 6
j
A
⋅
B
= 8 – 18 = 26
2
2
2
2
2
3
3.6
4
6
7.2
26
cos
1
3.6 7.2
A
B
A B
A
B
θ
=
+
=
=
+
=
⋅

=
=
= 
⋅
×
θ
= cos
1
= 180
o
2.
A force
F
= 3 N
i
– 5 N
j
produces a displacement on a particle given
by
s
= 5 m
i
– 2 m
j
. Find the work done by the force.
F
= 3 N
i
– 5 N
j
,
s
= 5 m
i
– 2 m
j
.
W = F
⋅
s = 15 + 10 =
25 J
3.
What is the work done to raise a 50kg box to a height of 3.0 m?
The force needed to raise the box is its weight = 50
×
9.8 = 490 N
W = F
⋅
y
= 490 N
×
3.0 m = 1470 J
4.
A tractor exerts a constant force of 4.5
×
10
4
N in moving a load
horizontally a distance of
150 m. (i) What is the work done? (ii) If the
tractor does this work in 45 s, what is the power developed by its
engine?
(i)
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Fall '10
 George
 Physics, Force, Work, 2.2 m, 100 J, 5.0kg, 4.9 k

Click to edit the document details