A child drops a toy from the top of a building, it takes 1 s to reach the ground. Find the height of the building and the average speed of the toy respectively. (Take g = 10ms−2)
A
4mand5ms−1
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B
5mand5ms−1
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C
6mand6ms−1
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D
7mand7ms−1
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Solution
The correct option is B5mand5ms−1 Given: Initial velocity, u=0 Acceleration due to gravity, g=−10ms−2 Time taken, t=1s Upward direction is taken as positive.
Let the height of the building be H. Displacement will be: s=−H
Using second equation of motion, s=ut+12at2 −H=0+12×(−10)×12 H=5m
Average speed of a body is the ratio of total distance travelled to the total time taken. <v>=|s|t <v>=51=5ms−1