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Physics 221
test 1 key concepts
| Term | Definition |
|---|---|
| Instantaneous Speed | magnitude of the instantaneous velocity. |
| Average Acceleration | Whenever the velocity of an object is changing, then the object is accelerating. a = ∆v/∆t. a vector. |
| Instantaneous Acceleration | a(t) = ∆v/∆t as ∆t becomes infinitesimally small; is equal to the slope of the velocity versus time graph at time t. |
| Newton’s 2nd law | F=MA Unbalanced forces cause acceleration. no net force <--> no acceleration - F = ma. =vector |
| Weight | Fg = mg. We also have Fg = ma from Newton's second law, so g = a. The proportional constant g is called the acceleration due to gravity. |
| Hooke's Law | F = -kx. |
| Work | W = F·d. |
| Power | P = ∆W/∆t = average power |
| Projectile Motion | v = v0 + a∆t; motion of a particle through a region of tree-dimensional space where it is subject to constant acceleration; The trajectoryis a parabola. |
| Uniform circular Motion | An object moving in a circle of radius r with constant speed v is accelerating. The magnitude of the centripetal acceleration vector is ac = v2/r. |
| if the displacement vector is zero then the average velocity is | zero |
| Whenever your velocity is CHANGING | you are accelerating (If your velocity is NOT changing, then, no matter haw fast you are moving, you are NOT accelerating.) |
| In one dimension, if the x-component of a vector is positive | the vector is pointing in the positive x-direction. |
| For motion with constant acceleration in one dimension the velocity versus time graph is a | straight line |
| In SI units | mass = kg, acceleration = m/s2 force = (N). 1 N = 1 kg·m/s2. |
| Near the surface of the earth g is the same for all objects; therefore, | All objects accelerate at approximately the same rate. |
| If the net force acting on an object is constant, then the object's acceleration is constant. | If the net force is zero, the acceleration is zero and the object's velocity does not change. |
| A car travels in a straight line covering a total distance of 90.0 miles in 60.0 minutes. Which of the following must be true? | The average velocity of the car is 90.0 mi/hr in the direction of motion. |
| What is the direction of the acceleration vector if the bunny is moving to the left? | In the positive x‐direction |
| Which one of the following situations is not possible? | A body travels with a constant velocity and a time‐varying acceleration. |
| Suppose an ice skater is moving on the surface of a frozen lake at constant velocity. What is true about the external (outside) forces acting on the skater? | There could be some but they all cancel out. |
| Suppose you are standing on a bathroom scale when you are flying in a jet airplane. For a moment the scale reads less than your actual weight. During that moment, the scale is exerting an upward force on you that is | less than your weight. |
| A woman exerts a constant horizontal force on a large box. As a result, the box moves across a horizontal floor at a constant speed. The constant horizontal force supplied by the woman | has the same magnitude as the total force which resists the motion of the box. |
| If the women suddenly stops applying a horizontal force to the box, then the box will | immediately start slowing to a stop. |
| A bowling ball rolls down an alley and hits a bowling pin. Which statement below is true about the magnitudes of the forces exerted during the impact? | The magnitudes of the forces that they exert on each are equal. |
| If you push on a friend and he is accelerating away from you, how will the force you exert on your friend compare to the force your friend exerts on you? | The forces are equal in magnitude. |
| Consider a car at rest. We can conclude that the downward gravitational pull of Earth on the car and the upward contact force of Earth on it are equal in magnitude and opposite in direction because | the net force on the car is zero. |
| Which of the position versus time graphs represents motion with constant acceleration? | all of them with positive slopes |
| Your friend asks you to stand perfectly still holding up a weight bar with weights while he takes a picture. Are you doing work during this time? | no |
| A woman exerts a constant horizontal force pulling a box across a rough floor at a constant speed. What can you say about the work done by friction? | Friction does negative work. |
| Vector A has magnitude 10 and vector B has magnitude 12. What is NOT a possible magnitude of vector C = A + B? | 25 |
| A heavy box sits in the back of a pickup truck. The truck and the box are accelerating towards the left. What is the direction of the frictional force on the box? | towards the left |
| When sliding a heavy box across the floor, it is often times helpful to lift up on it slightly because | you are lessening the friction force by reducing the normal force the floor exerts on the box. |
| Some engineers have suggested that we can simulate gravity in outer space by having a circular rotating space station where persons feel an outward‐directed fictitious force due to the rotation of the station. The reason they feel such a force is because | 2. they are accelerating toward the center of the space and the walls of the space station provide the centripetal force, which they experience as an apparent weight |
| Which of the following statements about vectors and scalars are TRUE? | e. A vector quantity has a direction and a scalar does not. |
| Which of the following statements about distance and/or displacement are TRUE? | If a person walks in a straight line and never changes direction, then the distance and displacement = same. |
| Which of the following statements about velocity and/or speed are TRUE? | Velocity= vector quantity and speed= scalar quantity; average velocity of an object on a round-trip journey = 0; Joe moves from A to B in 5 seconds. Bo moves between the same two locations in 10 seconds. The velocity of person X is twice that of person Y |
| The acceleration of an object is equal to | b. the rate of change of its velocity. |
| An elevator is being lifted up an elevator shaft at a constant speed by a steel cable as shown in the figure above. All frictional effects are negligible. In this situation, forces on the elevator are such that | b. the upward force by the cable is equal to the downward force of gravity |
| If we could eliminate air resistance, would a light sheet of paper and a heavy book accelerate at the same rate, if dropped from a fourth floor window? | They both would accelerate downward with g = 9.8 m/s2; same rate |
| miles/hour | 1609meters/3600seconds |
| A stone is dropped from the roof of a single story building to the surface of the earth. | c. It speeds up because of an almost constant force of gravity acting upon it. |
| You are watching a semi truck bounce up and down on a spring. (Yep it’s a toy.) At the topmost point in the truck’s path | the truck’s velocity is zero but its acceleration is downward |
| Two metal balls are the same size but one weighs twice as much as the other. The balls are dropped from the roof of a single story building at the same instant of time. The time it takes the balls to reach the ground will be | c. about the same for both balls. |
| In order to do a positive amount of work you must | exert a force and move in the direction of the force |
| A child is riding a bike and skids to a stop. What happens to their kinetic energy? | It is converted into thermal energy |
| Suppose Larissa throws a ball up in the air and it comes back down to the same place she threw it from. Ignore the times when the ball is in contact with her hand, and ignore air resistance. | The ball has minimum kinetic and maximum potential energy at maximum height |
| Three trajectories labeled A, B, and C are shown below. For which trajectory is the vertical velocity component at launch the greatest? | All three trajectories have the same initial vertical velocity component at launch. All three trajectories have the same height. |
| maximum force of static friction | between two surfaces is roughly proportional to the magnitude of the force pressing the two surfaces together. |
| add and subtract the components of vectors | Sx =Ax +Bx +Cx, Sy =Ay +By +Cy S=sqrt(Sx2 +Sy2) |
| Work can convert other forms of energy into gravitational potential energy. | Work = mgh |
| The centripetal acceleration points towards the center of the circle. | The magnitude of the centripetal acceleration vector is ac = v2/r. |
| The angular frequency ω is given by ω | ω = 2π/T. The angular frequency is measured in radians per second. |
| The inverse of the period is the frequency | f = 1/T. |
| Power | work/time = mgh/t |
| Whenever the force and the displacement are in the same direction, you do | positive work |
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baverwat