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A ball is thrown at an angle of 60 degrees to the horizontal and lands 90 m away on level ground. If the same ball is thrown with the same initial speed at an angle of 30 degrees to the horizontal, how far will it land?

1. 120 m
2. 90 m
3. 60 m
4. 30 m

Correct answer: 90 m

Solution

The range depends on sin(2*theta). For theta=60: 2*theta=120 deg, sin(120)=sin(60). For theta=30: 2*theta=60 deg, sin(60). Both give the same value. Therefore the range is unchanged at 90 m. This is the complementary angle property of projectile motion (angles that sum to 90 deg give equal ranges).

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