Final answer:
To find how long a rock falls before hitting the ground with a final velocity of 85 m/s, we use the kinematic equation v = u + at and find that it falls for approximately 8.67 seconds.
Step-by-step explanation:
The student is asking how long a rock would fall before hitting the ground if its final velocity was 85 m/s. This is a physics question relating to falling objects within the field of mechanics. We can use the kinematic equation for uniformly accelerated motion to find the time it took for the rock to reach the ground. The relevant kinematic equation is:
v = u + at
Where:
- v is the final velocity (85 m/s in this case)
- u is the initial velocity (0 m/s since the rock falls off the cliff)
- a is the acceleration due to gravity (approximately 9.8 m/s2)
- t is the time in seconds
Rearranging the equation to solve for time (t) gives us:
t = (v - u) / a
Plugging in the values:
t = (85 m/s - 0 m/s) / 9.8 m/s2 = 8.67 seconds
The rock would therefore fall for about 8.67 seconds before hitting the ground.