DYNAMICS & FREE-BODY DIAGRAMS
A block rests on a horizontal table. A student claims the normal force and gravitational force form a Newton's Third Law pair. Explain why this statement is incorrect.
What is because both forces act on the same object rather than on two different interacting objects?
An object has positive velocity and positive acceleration. Describe its motion.
What is it is speeding up in the positive direction?
An object slides down a frictionless ramp. Explain why the normal force does no work.
What is because the normal force is perpendicular to the displacement?
A rubber ball and a lump of clay strike a wall with equal speed. The rubber ball rebounds while the clay sticks. Which experiences the greater impulse magnitude?
What is the rubber ball?
Rotational inertia depends not only on mass but also on this property.
What is how the mass is distributed relative to the axis?
A box is pushed up a rough incline at constant speed. Describe the net force parallel to the incline and explain why.
What is the net force parallel to the incline is zero because the acceleration is zero?
The slope of a tangent line on a position vs. time graph represents this quantity.
What is instantaneous velocity?
A student lifts a backpack vertically at constant speed. Compare the work done by gravity and the work done by the student.
What is they are equal in magnitude and opposite in sign?
Why can a small force applied over a long time produce the same impulse as a large force applied briefly?
What is because impulse depends on the product of force and time interval?
A force is applied directly through the pivot point of a door. Explain why the torque is zero.
What is because the lever arm distance is zero?
A pendulum swings through its lowest point. Compare the tension force to the weight of the bob at that instant.
What is the tension force is greater than the weight because centripetal acceleration is upward?
Two students analyze a velocity vs. time graph. One says the object moved because velocity is positive; the other says displacement is zero because positive and negative areas cancel. Which student is correct?
What is both students are correct?
A cart rolls into a spring on a frictionless track. At maximum compression, what quantities must be zero and nonzero?
What is velocity is zero while acceleration and spring force are nonzero?
During an explosion, two fragments move apart. Explain why the center of mass continues along the original path.
What is because the explosion forces are internal to the system?
A hoop and a solid sphere roll down the same incline from rest. Explain why the sphere reaches the bottom first.
What is the sphere has less rotational inertia relative to its mass?
Two blocks are connected by a string on a frictionless surface. A horizontal force is applied to the first block. Explain why the tension force is smaller than the applied force.
What is because part of the applied force accelerates the first block itself?
A ball is thrown upward from a cliff. Neglecting air resistance, compare the magnitude of the acceleration at the top of the trajectory and halfway down.
What is the acceleration magnitude is the same at both points?
A pendulum released from rest swings downward. Explain why tension does not transfer energy to the bob.
What is because the tension force is always perpendicular to the displacement?
A moving cart collides with an identical stationary cart and they stick together. Compare the system kinetic energy before and after the collision.
What is kinetic energy decreases?
A spinning figure skater pulls in her arms. Explain why her rotational speed increases.
What is conservation of angular momentum requires angular speed to increase as rotational inertia decreases?
A student argues that an object moving in a circle at constant speed is in equilibrium because its speed does not change. Identify the flaw in the reasoning.
What is the object is accelerating because its direction changes continuously, so the net force is not zero?
A motion detector records position increasing linearly with time. Later the graph curves upward. Interpret the physical meaning of the change in graph shape.
What is the object changes from constant velocity motion to positive acceleration?
A block slides across a rough horizontal surface and stops. Explain where the original kinetic energy goes.
What is it is transformed into thermal energy within the block and surface?
A student claims momentum is conserved in every collision. State the missing condition required for this statement to be true.
What is the net external force on the system must be negligible?
A satellite orbits Earth in an ellipse. Explain why the satellite moves fastest near periapsis.
What is conservation of angular momentum causes higher speed at smaller orbital radius?