# Kinematics: a question about a falling mollusc.

• raphile
In summary, the problem involves a crow dropping a mollusc at a height of 28.8m above the ground with a speed of 2m/s. By using the gravitational acceleration and ignoring air resistance, the velocity of the mollusc at impact is found to be 23.855m/s at an angle of 85.2 degrees below the horizontal. The second part of the problem involves finding the horizontal and vertical components of the average force acting on the 20-gram mollusc after impact, which are calculated to be -0.8N and 17.85N respectively.
raphile
Hey, I have an answer to this problem but really need someone to look through it and see if I've used the right method. I have an exam in a few days! Thanks :)

## Homework Statement

A crow drops a mollusc when moving with speed 2m/s in a level flight at a height of 28.8m above rocky ground. By taking the gravitational acceleration to be 9.81m/s^2 and ignoring air resistance, specify the velocity of the mollusc in magnitude and direction on its impact with the ground.

If the mass of the shellfish is 20 grams and the duration of the impact is 0.03s, find the horizontal and vertical components of the average force that acts on the shell if the forward and upward components of the velocity of the mollusc after impact are 0.8m/s and 3m/s respectively.

## The Attempt at a Solution

The horizontal speed of the mollusc remains constant at 2m/s during the fall.
To find the vertical speed, first find the duration of the fall:
using s=ut+(1/2)at^2 we have 28.8 = (1/2*9.81*t^2) => t = 2.423 seconds.
Hence the vertical speed at impact is, using v=u+at: (0+(9.81*2.423)) = 23.77m/s.
So the magnitude of the speed at impact is sqrt(2^2+23.77^2) = 23.855m/s.
And the direction is arctan(23.77/2) = 85.2 degrees below the horizontal.

Now onto the second part...

The acceleration horizontally is (change in velocity divide time) = (0.8-2)/0.03 = -40. Hence the force acting forward is (mass times acceleration) = -0.8N.
The acceleration vertically is, using the same method, (3-(-23.77)/0.03 = 892.33. Hence the force acting upward is (892.33*0.02) = 17.85N.

Is this right? Please do check it, as I'm not convinced by the numbers I've got and my tutor is currently unavailable to help. Thanks.

I can't find anything wrong with it

Yes, your answers are correct.

## 1. What is kinematics?

Kinematics is a branch of mechanics that studies the motion of objects without considering the causes of motion. It focuses on the position, velocity, and acceleration of objects.

## 2. How does kinematics apply to a falling mollusc?

In the case of a falling mollusc, kinematics can be used to calculate the position, velocity, and acceleration of the mollusc as it falls. This information can help us understand the motion of the mollusc and predict its trajectory.

## 3. What factors affect the kinematics of a falling mollusc?

The kinematics of a falling mollusc can be affected by factors such as gravity, air resistance, and the shape and size of the mollusc. These factors can influence the acceleration and velocity of the mollusc as it falls.

## 4. How can we calculate the kinematics of a falling mollusc?

The kinematics of a falling mollusc can be calculated using equations such as the kinematic equations, which relate the position, velocity, acceleration, and time of an object. These equations can be solved using the known values of the mollusc's motion.

## 5. What are some real-world applications of kinematics?

Kinematics has many real-world applications such as predicting the trajectory of a projectile, analyzing the motion of vehicles, and understanding the movement of celestial bodies. It is also used in fields such as engineering, robotics, and sports science.

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