Aptitude Discussion

Q. |
A jet plane is rising vertically with a velocity of 10 m/s. It has reached a certain height when the pilot drops a coin, which takes 4 sec to hit the ground. Assuming that there is no resistance to the motion of the coin, the height of the place and the velocity of the coin on impact with the ground are: |

✖ A. |
38.4 m, 28.7 m/s |

✔ B. |
38.4 m, 29.2 m/s |

✖ C. |
26.5 m, 13.5 m/s |

✖ D. |
26.5 m, 28.7 m/s |

**Solution:**

Option(**B**) is correct

The coin will move up with the initial velocity of 10 m/s till it comes to rest. Time taken is given by:

$0=10−9.8t$

\(\Rightarrow t=\dfrac{10}{9.8}\) sec

Time taken to reach the ground from the highest point:

\(=4-\dfrac{10}{9.8}\)

\(=\dfrac{29.2}{9.8}\) sec

Velocity of coin on impact

\(=0+9.8\times \left(\dfrac{29.2}{9.8}\right)\)

$= 29.2$ m/s

If '$h$' is the height from which the coin dropped.

Then

\(29.2^2-10^2=2\times 9.8\times h\)

$⇒ h$ = **38.4 m**

**VENI**

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I cannot understands this problem .pls explain its simply.