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Both hit the water at the same time. Both hit the water with the same impact speed.

Two identical balls are thrown simultaneously from a bridge at 20 m/s. Ball A has an initial trajectory angle of 30° above the horizontal; ball B, 30° below the horizontal. Assuming no air drag (and constant g ), what will you see?. Both hit the water at the same time.

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Both hit the water at the same time. Both hit the water with the same impact speed.

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  1. Two identical balls are thrown simultaneously from a bridge at 20 m/s. Ball A has an initial trajectory angle of 30° above the horizontal; ball B, 30° below the horizontal. Assuming no air drag (and constant g), what will you see? • Both hit the water at the same time. • Both hit the water with the same impact speed. • Both reach the same maximum height. • Both move the same horizontal distance before impact. • More than one of the above. Oregon State University PH 211, Lecture #8

  2. You’re on the surface of planet Irth, where they haven’t yet invented calculators, but fortunately the acceleration due to gravity is 10.0 m/s2. You kick a stone horizontally off a cliff at an initial velocity of 40.0 m/s and it lands at an impact angle of –45.0° on the level ground below the cliff. How high is the cliff? 1. 20.0 m 2. 40.0 m 3. 80.0 m 4. 120 m 5. None of the above. Oregon State University PH 211, Lecture #8

  3. A hot air balloon rises at speed v. The balloonist hurls a ball horizontally outward at v0in his frame of reference. Which path best represents the path of the ball in the Earth’s frame? Oregon State University PH 211, Lecture #8

  4. Relative Motion: vAC =vAB+ vBC vBC = “the velocity of B relative to C” = “the velocity of B with respect to C” = “the velocity of B from C’s point of view” Note: vBC = – vCB Common examples: • Motion in a moving medium (water, air, etc.). • Impact speed when two moving objects collide. Oregon State University PH 211, Lecture #8

  5. Motion in a moving medium You can row a boat through water at 1.8 m/s. What is the minimum time you’ll need to reach the opposite shore directly across from your starting point on a river that’s 150 m wide and flowing at a uniform 0.60 m/s? Work in groups and be prepared to justify your answer. Oregon State University PH 211, Lecture #8

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