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Two bodies A and B are thrown simultaneously. A is projected vertically upwards with 20 m/s speed from ground and B is projected vertically downwards from a height of 40 m with the same speed and along the same line of motion. At what point do bodies collide?

15.1 m from the top(40m above ground) after 3s 17.3 m from ground after 2s 15.1 m from ground after 1s 16.5 m from the top(40m above ground) after 2s

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1 solution

Swapnil Rajawat
Aug 24, 2014

The relative acceleration between the two bodies is always zero. So we can apply the concept of relative velocity here. The relative velocity between the two bodies is always 40 m/s (Adding both the velocities). So, from s=ut | 40=40t therefore t=1 sec. The only option that have that value is d.

that's not the correct answer

Hemant Sharma - 5 years, 1 month ago

let h be height from the bottom .. so height from the top will be 40 - h............ velocities are same thus u(from bottom) and u(from top) are equal .............. h = 20t - 0.5gt^2 (from bottom g will be negative )............. 40 - h = 20t + 0.5gt^2............ Adding ... 40 = 2 20 t....... t = 1....... substituting t=1...... h = 20 - 4.9 = 15.1

Arjun Praveen - 5 years ago

good solution !!

Mayank Holmes - 6 years, 9 months ago

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