1. correct answer, O if not attempted and -1 if not correct. A ball is dropped from a building of height 45m. Simultaneously another ball is thrown up with a sp

1. correct answer, O if not attempted and -1 if not correct. A ball is dropped from a building of height 45m. Simultaneously another ball is thrown up with a speed 40m/s. The rate of change of relative speed of the balls is
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