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Physics: Newton’s Laws of Motion Study Guide
Name_______________________________
Date________
1. Define the first law of motion.
Objects at rest remain at rest, and objects in motion remain in motion in a
straight line at constant speed unless acted upon by an outside force.
2. What is the other name for the first law of motion?
The Law of Inertia
3. What is the amount of force needed to keep a fired cannon ball moving in
frictionless space?
Zero – because of Newton’s 1st Law of Motion it will keep going until an outside
force acts on it
4. How much will a 10 kg object weigh on the moon?
W=mg
W=10kg(1.67 m/s2)
W=100 N
5. How much mass will a 10 kg object have on the moon?
10 kg – the mass doesn’t change with location
6. What is the mass of a 100 N dog?
W=mg
100 N = m (10 m/s2)
Divide both sides by 10 m/s2
10 kg = m
7. Describe friction.
It is the force that opposes motion with two objects are in contact with each
other caused by the microscopic grooves on the surfaces of the objects.
8. A 10 N force and a 30 N force act on an object in opposite directions. What is
the net force on the object?
30 N – 10 N = 20 N (subtract since they are acting in opposite directions)
9. A 10 N force and a 30 N force act on an object in the same direction. What is
the net force on the object?
30 N + 10 N = 40 N (add since they are acting in the same direction)
10. Describe equilibrium.
When all the forces acting on an object add to zero and the object is either at rest
or traveling at a constant velocity
11. When a person stands on a scale with both feet on the scale, the scale reads
500 N. When she lifts one foot, what does the scale read?
500 N
12. In what direction does friction act?
Opposite the motion of the object
13. What is the maximum possible resultant when adding a 2 N force to a 6 N
force?
2N + 6 N = 8 N (add to get the biggest number possible)
14. What is the minimum possible resultant when adding a 2 N force to a 6 N
force?
6 N – 2 N = 4 N (subtract to get the smallest possible answer)
15. Which has more mass a kilogram of feathers or a kilogram of lead?
They have the same mass since a kilogram is a kilogram no matter what material
is being measured
16. How much does a 1 kg bag of nails weigh?
W=mg
W=(1kg)(10 m/s2)
W=10 N
17. An object weighs 40 N on earth. A second object weighs 40 N on the moon.
Which has the greater mass?
The object on the moon has the greater mass since the moon’s acceleration of
gravity is so much smaller than earth’s
18. What produces accelerations?
Forces
19. A heavy person and a light person parachute together and wear the same size
parachutes. Assuming they both open their parachutes at the same time, which
person reaches the ground first?
The heavy person reaches the ground first since they reach their terminal velocity
later than the lighter person
20. Suppose the force of friction on a sliding object is 10 N. The force needed to
maintain a constant velocity is (10 N, more than 10 N, or less than 10 N).
10 N (since it is at constant velocity it is in equilibrium so the force pushing the
object and the force of friction must combine to be zero)
21. What is the net force on an 1 N apple when it is in free fall?
1N since the only force acting on the apple is its weight
22. A girl pulls on a 10 kg wagon with a constant force of 30 N. What is the
wagon’s acceleration?
F=ma
30 N = 10 kg (a)
Divide both sides by 10 kg
A= 3 m/s2
23. A block is dragged without acceleration in a straight-line path across a level
surface by a force of 6 N. What is the frictional force between the block and the
surface?
Friction = 6 N because it is in equilibrium
24. A tennis ball and a stainless steel ball of the same size are dropped at the same
time. In the absence of air resistance, which ball has the greater acceleration?
Both would have the same acceleration since both are being accelerated by
gravity
25. If the force acting on a cart doubles, what happens to the cart’s acceleration?
It doubles since they are directly proportional
26. A car has a mass of 1500 kg and accelerates at 3 m/s/s. What is the magnitude
of the force acting on the car?
F=ma
F= (1500)(3)
F=4500 N
27. A truck exerts a force of 2000 N on a car, accelerating it at 2 m/s/s. What is
the mass of the car?
F=ma
2000=(m)(2)
Divide both sides by 2
M=1000 kg
28. You pull horizontally on a 50 kg crate with a force of 500 N, and the friction
force on the crate is 250 N. The acceleration of the crate is _________.
Total force = 500 – 250=250 N since friction acts opposite the motion of the
object
F=ma
250=(50)(a)
Divide both sides by 50
A= 5 m/s2
29. T/F Whenever an object exerts a force on another object, the second object
exerts a force of the same magnitude, but in the opposite direction to that of the
first object.
True that is Newton’s 3rd Law of Motion
30. Define action/reaction pairs.
Equal and opposite forces
31. As a ball falls, the action force is the pull of the earth’s mass on the ball.
What is the reaction force?
The ball’s mass pulling on the Earth
32. An unfortunate bug splatters against a windshield of a moving car. Compared
to the force of the car on the bug, the force of the bug on the car is (same, larger,
smaller).
The forces are the same because of Newton’s 3rd Law of Motion
33. Define Newton’s Third Law of Motion.
For every action there is an equal and opposite reaction.