Solve the problem.
-At about what velocity do you enter the water if you jump from a 15 meter cliff? (Use $g = 9.8 \mathrm {~m} / \mathrm { sec } ^ { 2 }$.)
A) $- 17 \mathrm {~m} / \mathrm { sec }$
B) $- 8.5 \mathrm {~m} / \mathrm { sec }$
C) $17 \mathrm {~m} / \mathrm { sec }$
D) $2 \mathrm {~m} / \mathrm { sec }$

Question

Quizplus · Accepted Answer

Using the equation of motion for free fall:
$$h = \frac{1}{2}gt^2$$
Where h is the height of the cliff and g is the acceleration due to gravity. We can solve for t:
$$t = \sqrt{\frac{2h}{g}} = \sqrt{\frac{2(15~\mathrm m)}{9.8~\mathrm {m/s^2}}} \approx 1.77~\mathrm s$$
Now, using the equation for velocity in free fall:
$$v = gt$$
We can solve for v:
$$v = g t = (9.8~\mathrm {m/s^2})(1.77~\mathrm s) \approx -17.4~\mathrm {m/s}$$
Note that the negative sign indicates that the velocity is downward (towards the water). Rounded to one decimal place, the answer is approximately $-17~\mathrm{m/s}$, which corresponds to choice A).

Solve the Problem g=9.8 m/sec2g = 9.8 \mathrm {~m} / \mathrm { sec } ^ { 2 }g=9.8 m/sec2

Solve the Problem $g = 9.8 \mathrm {~m} / \mathrm { sec } ^ { 2 }$