Each of the strobe photographs (a), (b), and (c) in Figure OQ2.18 was taken of a single disk moving toward the right, which we take as the positive direction. Within each photograph, the time interval between images is constant.
(i) Which photograph shows motion with zero acceleration?
(ii) Which photograph shows motion with positive acceleration?
(iii) Which photograph shows motion with negative acceleration?
(i) Figure (b) shows motion with zero acceleration.
(ii) Figure (c) shows motion with positive acceleration.
(iii) Figure (a) shows motion with negative acceleration.
There should be no net external force exerted on an object that is travelling at a constant non-zero velocity. Otherwise, the object's motion (velocity) would have been adjusted.
In terms of both speed and direction, the rate at which velocity varies over time. If a point or an object moves in a straight line faster or slower, it is said to be accelerated.
(i) The figure (b) shows the discs have equal spacing.
This means it has constant nonzero velocity and constant zero acceleration.
Thus figure (b) shows motion with zero acceleration.
(ii) By observing all three figures, it is clear that figure (c) shows positive acceleration throughout the duration of time.
Thus figure (c) shows motion with positive acceleration.
(iii) Figure (a) shows negative (leftward) acceleration in the first four images.
So, (a) is the correct option.
In a women’s 100-m race, accelerating uniformly, Laura takes 2.00 s and Healan 3.00 s to attain their maximum speeds, which they each maintain for the rest of the race. They cross the finish line simultaneously, both setting a world record of 10.4 s. (a) What is the acceleration of each sprinter? (b) What are their respective maximum speeds? (c) Which sprinter is ahead at the 6.00-s mark, and by how much? (d) What is the maximum distance by which Healan is behind Laura, and at what time does that occur?
Two thin rods are fastened to the inside of a circular ring as shown in Figure P2.84. One rod of length D is vertical, and the other of length L makes an angle with the horizontal. The two rods and the ring lie in a vertical plane. Two small beads are free to slide without friction along the rods. (a) If the two beads are released from rest simultaneously from the positions shown, use your intuition and guess which bead reaches the bottom first. (b) Find an expression for the time interval required for the red bead to fall from point A to point C in terms of g and D. (c) Find an expression for the time interval required for the blue bead to slide from point B to point C in terms of g, L, and . (d) Show that the two time intervals found in parts (b) and (c) are equal. What is the angle between the chords of the circle A B and B C? (e) Do these results surprise you? Was your intuitive guess in part (a) correct?
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