question in examkracker 1001 physics #194

[medscholhopeful]

there is an inclined plane diagram, if object m slides down the plane in 3s, what is the ratio of the distance it travels in the 1st second compares to the distance it travels in the 2nd second...seem easy enuf but still dont know how they got it.. this is my logic

using x=1/2at2, i divided x1/x2 = 1/2at2(for 1st second, t=1)/1/2at2(for second second t=2).. i came up with 1:4 but answer is 1:3 how come?.. thanks

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[ThirdEye]

Since it's a ratio, it will be the same ratio as if it was free falling for 3 sec.

After 1 second the velocity will be 10m/s and the avg. v is 5m/s... so it goes 5m in 1 sec.

After 2 seconds the velocity will be 20m/s. The avg v between 1 and 2 seconds is (10+20)/2 = 15m/s..... so it travels 15m from second 1 to second 2.

5:15 ----> 1:3

 

[medscholhopeful]

got it thanks!