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Unit 2: Homework Packet # 2
Newton’s 2nd Law (F = ma)
IMPORTANT INFORMATION to use in this packet!
A force is a push or a pull. To calculate force, we use the following formula:
F=ma
where F= force in Newton’s
m= mass in kg
a= acceleration in m/sec2
F
m
a
Weight is a force and can be measured in NEWTONs! Acceleration is 9.8 m/s 2 unless
otherwise mentioned.
Part 1: Force and Acceleration
1. With what force will a car hit a tree if the car has a mass of 3,000 kg and is accelerating at
a rate of 2 m/s2?
GIVEN
WORK
ANSWER
2. A 10 kg bowling ball would require what force to accelerate it down an alleyway at a rate of
3 m/s2?
GIVEN
WORK
ANSWER
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3. What is the mass of a falling rock if it hits the ground with a force of 147 Newton’s?
GIVEN
WORK
ANSWER
4. What is the acceleration of a softball if it has a mass of 0.50 kg and hits the catcher’s glove
with a force of 25 Newton’s?
GIVEN
WORK
ANSWER
5. What is the mass of a truck if it is accelerating at a rated of 5 m/s2 and hits a parked car
with a force of 14,000 Newton’s?
GIVEN
WORK
ANSWER
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Part 2: Newton’s Second Law, Net Force, and F=ma Problems
Directions: Answer the following questions on a separate piece of paper. Show all work
and formulas!
Formulas:
F = ma
Net Force = ma
Applied Force – Friction = Net Force
What is the definition of net force?
What is the mathematical formula for Newton’s 2nd Law?
What is the net force on a car at rest?
What is the net force on a car that is moving at a constant velocity?
If an object has a net force of zero, what is its acceleration?
What is the net force on an object with balanced forces?
What two things can you say about an object’s motion if the net forces on the object are zero?
Which of these objects are accelerating?
a. A ball that is falling.
b. A rocket flying at a constant velocity through space.
c. A car traveling down the road at a constant velocity.
d. A book resting on a table.
9. Which objects in #9 have zero net force?
10. The box below is moving to the right, but it is slowing down. Which force is bigger?
1.
2.
3.
4.
5.
6.
7.
8.
F1
F2
11. If the box above was moving to the right and speeding up, which force would have to be bigger?
12. If the box were moving to the left at a constant speed, which force would have to be bigger?
13. If it takes 4 N of force to keep a shopping cart moving at a constant velocity, what is the force of
14.
15.
16.
17.
18.
19.
20.
friction on the cart?
When you push something across the floor at a steady speed, you need to apply a force. Why?
Draw a diagram to help you explain your answer.
Using Newton’s 2nd Law, calculate the net force on an object with an acceleration of 5 m/s/s with a
mass of 100 kg.
A toy plane applies a thrust of 10 N of force. The air drag is 5 N. What is the net force on the
plane?
Is the plane in #16 accelerating?
A man has a mass of 60 kg. What does he weigh? Show work!
A small girl has a mass of 35 kg. What does she weigh? Show work!
Find the net force on the block below.
9N
6N
10 kg
21. If you push a 10 kg wagon with a net force of 20 N, what is the acceleration?
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22. What is the net force on the car below?
mass = 1000 kg
3000 N
23.
24.
25.
26.
27.
1000 N
What is the acceleration of the car above?
What is the acceleration of a 20 kg mass that has a net force of 100 N?
What is the acceleration of a 20 kg mass that has a net force of 200 N?
What is the acceleration of a 20 kg mass that has a net force of 50 N?
What is the acceleration of the system below? Which strings apply the greatest force?
1
5 kg
2
5kg
3
5 kg
30 N
28.
Friction = 300 N
500 N pull
200 kg
Net force = __________________
29.
a= 10 m/s/s
700 N
friction
Net force = __________________
300 kg
30.
a = 30 m/s/s
800 N
friction
500 kg
applied force
Applied force = ____________
31. The engine force of a car is greater then the force of friction. What can you say about the speed of
the car?
32. The engine force and the force of friction on a car are balanced. What can you say about the speed
of the car?
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Part 3: Adding and Subtracting Forces
Directions: Answer the following questions on a separate piece of paper. Show all work
and formulas!
Force in the same direction ………. ADD
Forces in opposite direction ……SUBTRACT
1. An ant pulls a seed with a force of 0.2 N. Another ant pulls in the opposite direction with a
force of 0.2 N. What is the net force?
2. If a slingshot shoots a 0.1 kg marble at an acceleration of 50 m/s/s, what was the force that
it applied?
3. If a bat hits a ball with a force of 40 N, and the ball’s acceleration is 50 m/s/s, what is the
mass of the ball in kg?
4. A mule pulls a plow north with a force of 200 N. The sliding friction on the plow is 100 N.
What is the net force?
5. In problem #4, if the mass of the plow is 50 kg, what is the acceleration of the plow?
6. Two mules pull the plow north with a force of 200 N each. The sliding friction of the plow is
100 N. What is the net force?
7. In problem #6, if the mass of the plow was 50 kg, what is the acceleration?
8. A dog pulls on its leash with 100 N towards the mailman. A boy pulls in the opposite
direction with a force of 90 N. What is the net force?
9. Two students are arm wrestling and neither is winning. One student is pushing with a force
of 59 N. What is the force of the other student?
10. A 20 kg robot is moving down the hall with a velocity of 2 km/hr, north. A scientist pushes
on the back of the robot with a force of 30 N. What happens to the velocity of the robot?
11. A 20 kg robot is moving down the hall with a velocity of 2 km/hr, north. A scientist pushes
on the robot’s right side with a force of 14 N. What happens to the velocity of the robot?
12. A 20 kg robot is moving down the hall with a velocity of 2 km/hr, north. A scientist pushes
on the front of the robot with a force of 14 N. What happens to the velocity of the robot?
13. Two teams are playing tug of war. One team pulls north with forces of 10 N, 30 N, and 50
N. The other team pulls south with forces of 45 N and 52 N. What is the net force?
14. Gravity pulls a statue on to its pedestal with a force of 345 N. What force is the pedestal
exerting and in what direction?
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Part 5: Car Crash Problems
F = ma
a = V2 – V1
t
Calculate the force on the car (C) and the wall (W).
M = 1000 kg
V1 = 50 m/s
V2 = 0 m/s
T = 0.1 sec
C=
1.
W=
M = 1000 kg
V1 = 100 m/s
V2 = 0 m/s
T = 0.1 sec
C=
2.
W=
M = 1000 kg
V1 = 50 m/s
V2 = 0 m/s
T = 0.05 sec
C=
3.
W=
M = 2000 kg
V1 = 50 m/s
V2 = 0 m/s
T = 0.1 sec
C=
4.
W=
M = 1000 kg
V1 = 50 m/s
V2 = 0 m/s
T = 10 sec
C=
5.
W=
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Part 6: Force Calculations
Directions: Solve the following problems. Show all of your work and the formulas that you
use to solve the problems. Remember to also include the correct units.
1. What is the force on a 1-kilogram ball that is falling freely due to the pull of gravity? (Neglect air
resistance.)
GIVEN
WORK
ANSWER
2. A man has a mass of 66 kilograms on the earth. What is his weight?
GIVEN
WORK
ANSWER
3. A girl on roller skates accelerates at a rate of 2 meters per second per second with a force of 100
Newton’s. What is her mass?
GIVEN
WORK
ANSWER
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4. A person weighs 540 Newton’s on the earth.
a.) What is the persons mass?
GIVEN
WORK
ANSWER
b.) What would the person weigh on the moon where the acceleration due to gravity is 1.67 Newton’s
per kilogram?
GIVEN
WORK
ANSWER
5. An elevator has a mass of 1000 kilograms.
a.) What is the tension force on its cables when it is stationary?
GIVEN
WORK
ANSWER
b.) What force is needed to accelerate it upward at a rate of 2 m/s/s?
GIVEN
WORK
ANSWER
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c.) What force is needed to accelerate it downward at a rate of 2 m/s/s?
WORK
GIVEN
ANSWER
6. A stationary car with a mass of 1500 kilograms reaches a velocity of 15 m/s, 5 seconds after starting.
a.) What is the car’s acceleration?
WORK
GIVEN
ANSWER
b.) How much force was required to reach this acceleration?
WORK
GIVEN
ANSWER
7. An astronaut has a mass of 50 kilograms.
a.) How much does she weigh before liftoff?
GIVEN
WORK
ANSWER
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b.) When her space vehicle is 6400 kilometers above the earth’s surface, she will weigh one
quarter (1/4) of what she weighed on earth.
(1) What does she weigh at that point in space?
GIVEN
WORK
ANSWER
(2) What is the acceleration on her mass at that point in space?
GIVEN
WORK
ANSWER
8. A 7000-kilogram plane is launched from an aircraft carrier in 2 seconds by a force of 350,000 Newton.
a.) What is the plane’s acceleration?
GIVEN
WORK
ANSWER
b.) What is the plane’s velocity?
GIVEN
WORK
ANSWER
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