PHY-102: Motion Exercises
Questions and answers
Complete the following exercises.
1. Jane is collecting data for a ball rolling down a hill. She
... [Show More] 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.
a. What is the independent variable in her experiment?
The ball would be the independent variable because it is not dependent on any other variable.
b. What is the dependent variable in her experiment?
The stopwatch would be the dependent variable because the time in which it stops on will be dependent on the distance in which the ball travels.
c. Give one control variable for her experiment.
The distances that the ball travels would be the control variable as the experimenter is in control utilizing varying distances to see how long it takes the ball to travel certain distances.
2. Consider an experiment where you drop an object.
a. Briefly describe your proposed experiment. (Make sure it is controlled).
For this experiment I will drop a pen and use a stopwatch on my phone to determine how long it takes to hit the ground from varying distances to the floor.
b. What would be the independent variable for your experiment?
The pen would be the independent variable because it is not dependent on any other variable.
c. What would be the dependent variable for your experiment?
The stopwatch on my phone would be the dependent variable because the time in which it stops on will be dependent on the distance in which the pen falls.
d. Give one control variable for your experiment.
The distance in which the pen falls will be the control variable as the experimenter is in control utilizing varying distances to see how long it takes the pen to hit the floor.
3. Consider a freely falling object.
A free-falling object would uniformly fall due to the force of gravity. The force of gravity has a standard acceleration formula
a. What is the acceleration (in m/s2) after 5 seconds of fall? 5 Seconds = 9.8 m/s2
b. What is the acceleration (in m/s2) after 10 seconds of fall?
10 Seconds = 9.8 m/s2
To determine the velocity of a free-falling object you would use the formula. velocity = acceleration * time
c. What is the velocity (in m/s) after 5 seconds of fall? 9.8 m/s * 5 Seconds = 49.0 m/s
d. What is the velocity (in m/s) of 10 seconds of fall? 9.8 m/s * 10 Seconds = 98.0 m/s
4. 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?
T= MG/2 = 350/2 = 175N
Each cable has a tension of 175N because the sign is hung in between the cables which is evenly distributing its weight to each cable.
5. 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.
a. What is the tension (in N) in the right cable?
T = 750N
b. Explain your answer.
The right cable would be 750N because the weight of the worker and plank equals 1300N. Since the left cable has 550N in tension, the right cable must hold the rest of the weights tension. Formula below:
-FNet = Ma = 0
-550 – 450 – 850 + T = 0 T = 750N
6. Two forces of 50 N and 30 N, respectively, are acting on an object. Find the net force (in N) on the object if …
a. the forces are acting in the same direction
When the forces of an object are acting in the same direction you would add them together to find the net force.
Net F = F1 + F2 = 50N + 30N = 80N
b. the forces are acting in opposite directions.
When the forces of an object are acting in opposing directions you would deduct them from one another.
Net F = F1 – F2 = 50N – 30N = 20N
7. A box is pulled straight across the floor at a constant speed. It is pulled with a horizontal force of 48 N.
a. Find the net force (in N) on the box. F_net = ma
Since the box is pulled at a constant speed its acceleration is 0. This would mean that F_net = 0.
b. Find the force of friction (in N) from the floor on the box. F_net = F – F_frict
Since the only force of friction is the box being pulled the force of friction, while in motion would equal 48N.
c. 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.
If the box came to a stop you would deduct the net force from the force of friction to determine the new force of friction when the box is at rest which, in this case would be, 0N.
8. A bowling ball rolls 32 meters in 0.8 seconds. Find the average speed (in m/s) of the bowling ball in m/s.
Average Speed = Distance / Time 32 Meters / 0.8 Seconds = 40m/s
9. 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.
Acceleration = (Final – Initial)Speed/Time (17m/s – 3.5 m/s)/4.5s = 3m/s2
10. Rank the following from lowest to highest:
a. The support force on you standing in an elevator at rest.
b. The support force on you standing in an elevator accelerating upward.
c. The support force on you standing in an elevator accelerating downward. 1. The support force on you standing in an elevator accelerating downward.
a. This would be the lowest since it is actually releasing tension.
2. The support force on you standing in an elevator at rest.
a. This would be the second since there is no tension.
3. The support force on you standing in an elevator accelerating upward.
a. This would be the highest since it is using much tension and force to pull the weight of the elevator. [Show Less]