Effects of forces on speed and direction Transitional Reasoning Download PDF

Questions

1. 1.

   During a physics seminar, a student proposes the hypothesis: "Whenever an unbalanced net force acts on a moving object, the object must change its direction of travel." To test this proposal, the student collects observations from several laboratory demonstrations. Which observation provides conclusive evidence that disproves the student's hypothesis?

   • A) A model train rounding a circular curve at a constant speed while guided by an inward horizontal force
   • B) A hover-puck drifting across a level table at a constant speed in a straight line with zero net force acting on it
   • C) A rolling steel sphere deflecting into a curved trajectory while accelerating under a diagonal push
   • D) A dynamic cart moving along a straight track that steadily increases its speed under a forward net force aligned with its line of travel
2. 2.

   A remote-controlled hovercraft glides forward in a straight line across a wide, frictionless testing floor at a constant speed, driven by a forward propulsion thruster of 40 N that exactly balances an opposing air-resistance brake of 40 N. The operator then reduces the forward thrust to 25 N while the 40 N opposing force remains constant and aligned along the line of motion. How do the hovercraft's speed and direction of travel change immediately following this adjustment?

   • A) The hovercraft immediately reverses its direction of travel and speeds up in the backward direction.
   • B) The hovercraft continues moving in the original direction at a constant speed because forward thrust is still applied.
   • C) The hovercraft veers off its straight-line path into a curve because the opposing forces are no longer balanced.
   • D) The hovercraft continues moving forward along its original straight-line path, while its speed decreases.
3. 3.

   During a physics demonstration, an air-hockey puck moves across a frictionless horizontal table, guided along a smooth circular path by a continuous inward horizontal force. At a specific instant, this guiding force is suddenly and completely removed, reducing the net horizontal force on the puck to zero. How do the speed and direction of travel of the puck change immediately after the force is removed?

   • A) The puck continues to curve along its circular path for a brief period before straightening, while its speed steadily decreases.
   • B) The puck veers radially outward away from the center of the original circle, while its speed remains constant.
   • C) The puck travels in a straight line tangent to the circular path at constant speed, with neither its speed nor its direction changing thereafter.
   • D) The puck travels in a straight line tangent to the circular path, while its speed steadily decreases because no forward force sustains its motion.
4. 4.

   A small sensor puck glides smoothly across a frictionless horizontal surface with an initial velocity directed due east. As it enters a specialized test area, a steady, constant net force directed due north is continuously applied to the puck. How do the puck's speed and direction of travel change while it moves through this area?

   • A) Its direction continuously curves toward the north, and its overall speed continuously increases.
   • B) Its direction continuously curves toward the north along a circular path, and its overall speed remains constant.
   • C) Its direction instantly turns to point due north, and its overall speed remains constant.
   • D) Its direction continuously curves toward the north, and its overall speed continuously decreases.
5. 5.

   During a physics laboratory investigation, students record three distinct trials of a robotic cart moving across a level surface: in Trial 1, the cart speeds up while keeping a straight-line path; in Trial 2, it curves along a circular arc at a constant speed; and in Trial 3, it turns along a curve while steadily slowing down. Which statement correctly identifies the orientation of the net force relative to the cart's direction of motion in all three trials?

   • A) In Trial 1, the net force is strictly perpendicular to motion; in Trial 2, it is in the direction of motion; and in Trial 3, it acts at an acute angle to motion.
   • B) In Trial 1, the net force is in the direction of motion; in Trial 2, it acts at an acute angle to motion; and in Trial 3, it is strictly perpendicular to motion.
   • C) In Trial 1, the net force is in the direction of motion; in Trial 2, it is strictly perpendicular to motion; and in Trial 3, it acts at an obtuse angle to motion.
   • D) In Trial 1, the net force is zero; in Trial 2, it is strictly perpendicular to motion; and in Trial 3, it acts directly opposite to motion.
6. 6.

   During a laboratory investigation on an air table, a puck glides horizontally in a straight line. A continuous, steady horizontal force is applied along its path, causing the puck to slow down to a momentary stop and then immediately travel backward along the same straight line with increasing speed. Which statement correctly characterizes the applied net force throughout this entire trial?

   • A) The net force acted opposite to the initial motion until the puck stopped, then reversed direction to propel it backward.
   • B) A perpendicular net force was applied at the turning point to rotate the puck's velocity vector into the reverse direction.
   • C) The net force continuously decreased and reached zero at the turning point because zero instantaneous speed requires balanced forces.
   • D) A constant net force directed opposite to the initial motion acted throughout, first slowing the puck to rest and then accelerating it in the reversed direction.
7. 7.

   An automated research sled travels forward in a straight line across a low-friction horizontal testing track. Test operators need to decrease the sled's speed while ensuring it continues moving forward along the exact same straight-line trajectory without veering. Based on the effects of forces on speed and direction, how must the net horizontal force be applied to the sled?

   • A) Perpendicular to the sled's direction of motion
   • B) Directly opposite to the sled's direction of motion
   • C) At an obtuse angle to the sled's direction of motion
   • D) In the same forward direction as the sled's motion
8. 8.

   During a laboratory trial on a frictionless air table, a sensor tracks a small disk moving initially in a straight line. Over a two-second interval, the disk maintains a strictly constant speed of 2.0 m/s while its trajectory bends into a smooth curve to the right. What does this observation reveal about the net horizontal force acting on the disk during this interval?

   • A) The net force must be zero because the speed of the disk does not change.
   • B) A constant net force acts directly in the forward direction of the disk's motion.
   • C) A non-zero net force acts perpendicular to the direction of motion, directed toward the right.
   • D) A net force acts in the direction opposite to motion, balancing the turning effect.
9. 9.

   A remote-controlled rover travels across a frictionless horizontal surface with a constant velocity directed due north. A continuous net horizontal force is suddenly applied to the rover pointing toward the southwest. Based on the orientation of this force relative to the rover's motion, what immediate changes occur in the rover's speed and direction?

   • A) Its speed decreases, and its direction deflects toward the west.
   • B) Its speed increases, and its direction deflects toward the west.
   • C) Its speed decreases, but its direction remains strictly toward the north.
   • D) Its speed remains constant, and its direction deflects toward the south.