Fundamentals of Motion and Forces in Physics
Complete the following exercises.
- Jane is collecting data for a ball rolling down a hill. She measures out a set of different distances and then proceeds to use a stopwatch to find the time it takes the ball to roll each distance.
- What is the independent variable in her experiment?
The ball
- What is the dependent variable in her experiment?
Time taken by the ball to roll each distance
- Give one control variable for her experiment.
The steepness of the hill
The height from which the ball is released on the hill
- Consider an experiment where you drop an object.
- Briefly describe your proposed experiment. (Make sure it is controlled).
To determine the time taken by the object to hit the ground.
- What would be the independent variable for your experiment?
The weight of the object.
2. What would be the dependent variable for your experiment?
The amount of distance it rolls when it hits the ground.
3.Give one control variable for your experiment.
The acceleration of the falling object.
- Consider a freely falling object.
- What is the acceleration (in m/s2) after 5 seconds of fall?
- 50m/s²
- What is the acceleration (in m/s2) after 10 seconds of fall?
- 100m/s²
- What is the velocity (in m/s) after 5 seconds of fall?
- 16.67m/s
- What is the velocity (in m/s) of 10 seconds of fall?
100 m/s\
33.33 m/s
can determinethe velocity and location of any free falling object at any time using the following equations.
V = a * t
10 m/s
- A sign is hung between two cables as illustrated below. If the sign weighs 350 N, what is the tension (in N) in each cable?
Let the left cable be T1 and right cable be T2.
The cables are in perpendicular position and hence each of them carries half the load.
Therefore,
T1 = T2 = 1/2W
T1=T2=1/2(350 N)
T1 = T2 = 175 N
- A construction worker on a high-rise building is on a platform suspended between two cables as illustrated below. The construction worker weighs 850 N, the plank weighs 450 N, and the tension in the left cable is 550 N. What is the tension (in N) in the right cable?
850 – 450 = 400 N
850 – 550 = 300
400 N + 300 N = 700 N
Explain your answer.
The tension in the right side is more than the tension in the left side since the weight of the constructor is more in that side.
- Two forces of 50 N and 30 N, respectively, are acting on an object. Find the net force (in N) on the object if …
- the forces are acting in the same direction
50N + 30 N = 80 N
- the forces are acting in opposite directions.
- – 30 N = 20 N
- A box is pulled straight across the floor at a constant speed. It is pulled with a horizontal force of 48 N.
- Find the net force (in N) on the box.
Zero
Find the force of friction (in N) from the floor on the box.
Ffr = -48 N
- The person pulling on the box stops pulling and the box comes to a rest. Find the force of friction (in N) on the box when at rest.
Zero
- A bowling ball rolls 32 meters in 0.8 seconds. Find the average speed (in m/s) of the bowling ball in m/s.
S = 32m
T =0.8 s
Average speed (V) = S/T (1)
Where s is all the way and t is all the time
Of (1) v = 32 m/0.8 s
V = 40 m/s
- A car accelerates from 3.5 m/s to 17 m/s in 4.5 seconds. Find the acceleration of the car in m/s2.
The change in velocity = 17 m/s – 3.5 m/s = 13.5 m/s
A = Dv/Dt
A = (13.5 m/s)/ (4.5 s)
A = 3 m/s²
- Rank the following from lowest to highest:
- The support force on you standing in an elevator at rest.
- The support force on you standing in an elevator accelerating upward.
- The support force on you standing in an elevator accelerating downward.
The support force on you standing in an elevator at rest
The support force on you standing in an elevator accelerating downward.
The support force on you standing in an elevator accelerating upward.
- Describe the speed and acceleration of the ball released from the top of the track shown in the figure below.
The speed increases as the ball goes down while the acceleration remains the same.
- Describe the speed and acceleration of the ball released from the top of the track shown in the figure below.
The speed increases as the acceleration remains constant.
- Describe the speed and acceleration of the ball released from the top of the track shown in the figure below.
The speed increases as the ball goes down while the acceleration remains the same
- You throw a ball upward with a speed of 14 m/s. What is the acceleration of the ball after it leaves your hand? Ignore air resistance and provide an explanation for your answer.
A = 9.8m/s²
The ball reaches the maximum height whereby the net force operating on it is zero and the force of gravity is normally 9.8m/s².
- How would your answer to the previous question change if you take into account the effects of air resistance?
The acceleration will remain the same
- Describe the speed and acceleration of a person sky diving. Include in your explanation a description of the motion before the parachute is opened as well as a description of the motion after the parachute is opened.
As the skydiver falls downwards, he accelerates hence gaining a speed in each second. As the speed increases the air resistance also increases. As he falls the force of air resistance equals the force of gravity and there is no more acceleration involved. Before the parachute is opened, the skydiver experiences less air resistance than when the parachute is opened. The open parachute enlarges the cross-sectional area of the skydiver hence an increased air resistance.
- A net force of 24 N is acting on a 4.0-kg object. Find the acceleration in m/s2
F = ma
24 N = (4.0 kg) (a)
a = 24n/4.0 kg
a = 6 m/s2
- A person pulls horizontally with a force of 64 N on a 14-kg box. There is a force of friction between the box and the floor of 36 N. Find the acceleration of the box in m/s2. Show your work.
A = F/M
A = (64 – 36)/14
A = 28/14
A = 2 m/s2
The remaining questions are multiple-choice questions:
- One difference between a hypothesis and a theory is that a hypothesis
- Is a guess that has not been well tested, whereas a theory is a synthesis of well-tested guesses.
- Is testable, whereas a theory is not testable.
- Can be revised, whereas a theory cannot be revised.
- Is not testable, whereas a theory is testable.
A: is a guess that has not been well tested, whereas a theory is a synthesis of well-tested guesses.
- A car starts from rest and reached a speed of 24 m/s in 6 seconds. What is the acceleration of the car?
- 144 m
- 6 m/s2
- 4 m/s2
- 10 m/s2
- 0 m/s2
C: 4 m/s2
- Which of the following forces is NOT a contact force?
- Friction force
- Support force
- Force of gravity
- Tension force
C:Force of gravity
- If you pull horizontally on a desk with a force of 150 N and the desk doesn’t move, the friction force must be 150 N. Now if you pull with 250 N so the desk slides at constant velocity, the friction force is
- more than 150 N, but less than 250 N.
- 250 N.
- more than 250.
A: more than 150 N, but less than 250 N.
- Suppose a particle is accelerated through space by a constant 10 N force. Suddenly the particle encounters a second force of 10 N in a direction opposite to that of the first force. The particle
- is brought to a rapid halt.
- theoretically accelerates to speeds approaching the speed of light.
- continues at the speed it had when it encountered the second force.
- gradually slows down to a halt.
C: Continues at the speed it had when it encountered the second force.
- Newton’s First Law of Motion applies to
- objects at rest only.
- moving objects only.
- both moving and non-moving objects.
C: both moving and non-moving objects
- A freely falling object starts from rest. After falling for 2 seconds, it will have a speed of about
- 5 m/s
- 10 m/s
- 20 m/s
- 40 m/s
C: 20 m/s
- Suppose an object is in free fall. Each second the object falls
- the same distance as in the second before.
- a larger distance than in the second before.
- with the same instantaneous speed.
- with the same average speed.
B: a larger distance than in the second before.