PHYS 2001

1
PHYS 2001
Spring 2009

• Relative Motion II. Newtons First Law
• III. Newtons Second Law

2
PHYS 2001
Spring 2009
vred 15 m/s
vblue 20 m/s
3
PHYS 2001
Spring 2009
vred 15 m/s
vblue -20 m/s
4
PHYS 2001
Spring 2009
CT1
If you are sitting in the red car, what would you
say the velocity of the red car is (i.e. what is
vr r )? 1. -15 m/s 2. -5 m/s 3. 0
m/s 4. 5 m/s 5. 15 m/s 6. 35 m/s
5
PHYS 2001
Spring 2009
EX1
A boat with a speed of 4.0 m/s crosses a 1800
meter wide river whose current is 2.0 m/s. How
fast does the boat travel relative to the shore
and how long does it take the boat to cross the
river?
6
PHYS 2001
Spring 2009
EX2
Two people try to move a 85-kg box across a room.
One person pushes on the box while the other
pulls horizontally on a rope that is tied around
the box. If one person pushes with a 120 N force
and the other pulls with a 150 N force and the
friction between the box and the floor is 70 N,
what is the acceleration of the box?
7
PHYS 2001
Spring 2009
CT2
What is the acceleration of a ball as it falls
towards the ground?
What is the acceleration of a ball that has been
thrown straight up as it rises towards the apex
of its trajectory?
What is the acceleration of a ball that has been
thrown straight up as it reaches the highest
point of its trajectory?
A. Up B. Down
8
PHYS 2001
Spring 2009
EX2
Two people try to move a 50-kg box across a room.
One person pushes on the box while the other
pulls horizontally on a rope that is tied around
the box. If one person pushes with a 120 N force
and the other pulls with a 150 N force and the
friction between the box and the floor is 70 N,
what is the acceleration of the box?
9
PHYS 2001
Spring 2009
EX3
Two people try to move a 50-kg box across a room.
One person pushes on the box while the other
pulls at an angle of 30 above the horizontal on
a rope that is tied around the box. If one
person pushes with a 120 N force and the other
pulls with a 150 N force and the friction between
the box and the floor is 70 N, what is the
acceleration of the box?