Question 115: Motion in 1D

Question

A ball is projected vertically upward with an initial velocity of 50 ms$$-$$1 at t = 0s. At t = 2s, another ball is projected vertically upward with same velocity. At t = __________ s, second ball will meet the first ball (g = 10 ms$$-$$2).

Accepted Answer

At t = 2 s, v
1
= 50 $$-$$ 2 $$	imes$$ 10 = 30 m/s
v
2
= v
2
$$	herefore$$ a
rel
= g $$-$$ g = 0
$$S = {{{u^2} - {v^2}} \over {2g}} = {{{{50}^2} - {{30}^2}} \over {2 	imes 10}} = {{1600} \over {20}} = 80$$ m
$$	herefore$$ v
rel
= 50 $$-$$ 30 = 20 m/s
$$	herefore$$ $$\Delta t = {{80} \over {20}} = 4\,s$$
$$	herefore$$ required time t = 2 + 4 = 6 s

Motion in 1D

A ball is projected vertically upward with an initial velocity of 50 ms$-1 at t = 0s. At t = 2s, another ball is projected vertically upward with same velocity. At t = __________ s, second ball will meet the first ball (g = 10 ms-$2).

Choose the correct answer: