Term 1 Questions Flashcards
Can an object have a varying speed if it’s velocity is constant? If yes, give examples.
An object cannot have a varying speed if it’s velocity is constant. In order for the velocity to be constant, both the magnitude and direction also has to be constant. Since velocity is a vector while speed is a scalar, the speed measuring the magnitude can never be different from the velocity/ an object’s speed is always shown in its velocity if it is constant.
Can an object have a varying velocity of its speed is constant? If yes, give examples.
An object can have a varying velocity if its speed is constant. Since velocity is a vector measurement while speed is a scalar, the velocity depend on its direction. For example, when a race car turns around the tracks at a constant speed of 10m/s, its velocity varies as the direction changes.
Can an object have a northward velocity and a southward acceleration? Explain.
Yes, an object can have a northward velocity and a southward acceleration. For example, when a car is slowing down/ put on brakes, its velocity is in the positive direction while its acceleration is in the negative direction. Thus, it is possible to move one direction while accelerating in the opposite direction.
Give an example where both the velocity and acceleration are negative.
A falling pencil has both a negative velocity and acceleration. Since the acceleration due to gravity is -9.8m/s^2 and the pencil is moving downward, its acceleration and velocity are both negative.
Two cars emerge side by side from a tunnel. Car A is traveling with a speed of 60km/h and has an acceleration of 40km/h/min. Car B has a speed of 40km/h/min and has an acceleration of 60km/h/min. Which car is passing the other as they come out of the tunnel? Explain your reasoning.
Car A passes car B as they come out of the tunnel. Since car A has a greater initial speed of 60km/h, it is initially traveling faster, thereby passing car B.
Is it possible for an object to have a negative acceleration while increasing in speed? If so, provide an example.
Yes, it is possible for an object to have a negative acceleration while increasing in speed. Since speed is a scalar quantity, it does not involve its direction. Therefore, a ball falling has an increasing speed in the negative direction due to gravity (negative acceleration).
As a freely falling object speeds up, what is happening to its acceleration due to gravity? Does it increase, decrease, or stay the same?
If there is no air resistance, its acceleration due to gravity stays the same. Since a freely falling object only has weight as a force acting upon it, mg = ma (the mass cancels out), its acceleration equals to gravity. Thus its acceleration is constant, staying at 9.8m/s^2.
How would you estimate the maximum height you could throw a vertically upward? How would you estimate the maximum speed you could give it?
- ) Throw a ball vertically upward and time how long it takes to come back down to the same initial height.
- ) Divide the time by 2 to get the time it takes for the ball to reach its apex.
- ) Plug the time into the equation dy = vit + 1/2 at^2, where vi is Om/s and a is 9.8m/s^2. Solve for distance.
- ) Plug the vertical distance and time into the equation v=d/t to solve for the velocity.
Can the displacement vector for an object moving in two dimensions ever be longer than the length of path traveled by the object over the same time interval? Can it be less? Discuss.
The displacement vector can be less than or equal to the length of path traveled over the same time interval, but never more. Since the displacement is the shortest distance from the starting point to the ending point while the path traveled is the exact distance traveled, a path that includes curves will always be longer. If the path was a straight line, however, it would have the same length as the displacement. Thus, the displacement will always be either the same or shorter than the actual path traveled.
During baseball practice, a batter hits a very high fly ball, and then runs in a straight line and catches it. Which had a greater displacement, the player or the ball?
The ball and the batter has the same displacement. Since displacement is the distance from the starting point to the ending point in a straight line, objects that start and end at the same point would have the same displacement. The batter and the ball both started and ended up at the same point so they both traveled the same displacement.
A projectile has the least speed at what point in its path?
A projectile has the least speed when it is at its apex. When an object travels a projectile, it’s vertical speed varies while its horizontal speed remains constant. As it is traveling upward, its speed decreases due to the negative acceleration of gravity until it reaches its highest point, where the vertical speed is at zero. When the object travels downward, its speed picks up in the negative direction. Therefore, the object has the least speed at its apex.
Why does a child in a wagon seem to fall backward when you give the wagon a sharp pull?
The child falls backwards when the wagon is pulled because the applied force on the wagon created friction on the child. According to newtons’ first law, an object in rest will stay in rest unless acted upon by an unbalanced force. Once the wagon is pulled, the parts of the child that is in contact with the wagon experiences friction pushing it forward while its head is at rest. So the child experiences more acceleration on the bottom which causes his/her head to seem as if he/she is falling backwards.
If the acceleration of a body is zero, are no forces acting on it?
No, there can be forces acting on an object even if there is no acceleration. According to Newton’s first law, an object at rest will stay at rest unless acted upon by an unbalanced force. An apple on the ground is at rest but experiences both weight and the normal force. Thus, if the forces are balanced, an object has no acceleration.
Only one force acts on an object. Can the object have zero acceleration? Can it have zero velocity?
No, an object with one force acting upon it can not have zero acceleration, but it can have a zero velocity. Based on Newton’s second law, the sum of all forces equals ma, a single force will always have an nonzero acceleration. When an object is thrown vertically upward, the only force acting on it is its weight and it has a vertical velocity of zero at its apex. Therefore, it is possible to have a zero velocity with one force acting upon it, but its acceleration can never be zero.
A stone hangs by a fine thread from the ceiling, and a section of the same thread dangles from the bottom of the stone. If a person gives a sharp pull on the dangling thread, where is the thread likely to break: below the stone or above it? What if the person gives a slow and steady pull? Explain your answers.
If a person gives a sharp pull, the string is likely to break below the stone. According to Newton’s first law, an object stays at rest unless acted upon by an unbalanced force, the rock is at rest. When the string is given a quick pull, the force is not translated to the upper part of the string and is unable to accelerate the rock. When the string is pulled slowly, the force gets translated to the top and it creates a greater net force at the top (more tension b/c weight + applied force). So the top of the string would be more likely to snap when pulled slowly.
