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Newton's First Law….The Law of Inertia
Ess HW 2.1
1. Does The Law of Inertia pertain to moving objects, objects at rest, or both? Support your
answer with examples.
2. Which has more inertia,
a. a bicycle or a truck?
b. a 10,000 kg truck parked at the side of the road or a 10,000 truck driving down the
freeway at 60 mph?
c. a parked truck or a Volkswagen bug traveling 150 mph?
3. If there are no forces acting on an object, can you conclude that it is not moving? WHY?
4. If an object is not moving, does that mean there are no forces acting on it? WHY?
5. Can an object go around a corner with no forces acting on it? WHY?
6. A 2 kg hockey puck is sliding across the frictionless ice at 6 m/s. How much force is
required to keep it moving at 6 m/s?
7. A car is driving down the road at a constant velocity of 30 mph.
a. What is the net force on the car?
b. What forces act on the car?
8. You push a large box across the floor at a constant velocity of 3 m/s.
a. What is the net force on the box?
b. What forces act on the box?
9. You push a large box across the floor at a constant velocity of 6 m/s.
a. What is the net force on the box?
b. What forces act on the box?
10. You are sitting at rest in a chair.
a. What is the net force on you?
b. What forces act on you?
11. Find the net force on each of the boxes shown below:
6N
10 N
A
10 N
6N
B
6N
6N
C
12. Suppose a box is sliding along a frictionless surface at 5 m/s.
a. What will the box do if no other forces act on it?
b. Suppose Roy got behind the box and pushed it forward with a force of 10 N. What would
the box do?
c. Suppose instead of Roy pushing the box forward, Sally got in front of the box and pushed
it backward with a force of 10 N. What would the box do?
d. What would the box do if BOTH Roy and Sally pushed the box at the same time? (BE
CAREFUL HERE AND THINK ABOUT NEWTON’S FIRST LAW!)
13. Suppose a box is sliding along the floor, and friction is resisting its motion with a force of
160 N. How much force do you need to exert to keep the box moving at a constant velocity?
14. Suppose Roy is driving his car at 60 mph and is not wearing his seatbelt. He is a bit sleepy,
and dozes off for a second, and crashes into a brick wall. He is thrown forward through the
windshield. (Don't worry, he's not hurt…Roy is particularly resilient.) Is there a force that
pushes Roy through the window? If so, what causes this force? If not, why does he go
through the window?
15. Many automobile passengers suffer neck injuries when struck by cars from behind. How
does Newton's law of inertia apply here? Why would a headrest help guard against whiplash?
16. If you were in a spaceship in the furthest depths of space, and you fired a cannonball into
space, what force would you have to exert on the ball to keep it moving?
17. a. Roy and Sally are fighting over a television set, which sits on a frictionless surface. Sally
pulls it to the left with a force of 120 N while Roy pulls to the right with a force of 90 N.
(Roy's feeling a bit weak after his recent car accident.) Find the net force on the TV
set.
b. What is the net force if there is no friction and Roy and Sally both push to the right?