Question #113613

Kinematics equations:

1. An angry scaffolder throws her spanner down to the ground with a velocity of 2 ms-1

the spanner takes 2 seconds to strike the ground.

Calculate the height the scaffolder was at when she threw down the spanner.

2. An experimental rocket is launched vertically with a velocity of 5ms-1

At a certain height the tail falls off and strikes the ground after 4 seconds.

Assuming the tail falls off while the rocket is travelling at 5 ms-1, calculate the height at which it

fell off.

1. An angry scaffolder throws her spanner down to the ground with a velocity of 2 ms-1

the spanner takes 2 seconds to strike the ground.

Calculate the height the scaffolder was at when she threw down the spanner.

2. An experimental rocket is launched vertically with a velocity of 5ms-1

At a certain height the tail falls off and strikes the ground after 4 seconds.

Assuming the tail falls off while the rocket is travelling at 5 ms-1, calculate the height at which it

fell off.

Expert's answer

**Explanation**

- Motion under gravity is applied here.
- Proper knowledge of the definitions of the terms used in the 4 basic equations (v=u+at..) is required.

Neglect the projectile appearance of the 2nd sketch & consider vertically.

**Calculations**

**1).**

"\\qquad\n\\begin{aligned}\n\\small \\downarrow s &= \\small ut + \\frac{1}{2}at^2\\\\\n\\small h&= \\small 2ms^{-1}\\times2s + 0.5\\times9.8ms^{-2} \\times (2s)^2\\\\\n&= \\small \\bold{23.6m}\n\\end{aligned}"

**2).**

"\\qquad\n\\begin{aligned}\n\\small \\downarrow s &= \\small ut + \\frac{1}{2}at^2\\\\\n\\small h &= \\small (-5ms^{-1})\\times 4s + 0.5\\times 9.8ms^{-2} \\times (4s)^2\\\\\n&= \\small \\bold{58.4m} \n\\end{aligned}"

Good Luck

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