Go Back   Physics Help Forum > High School and Pre-University Physics Help > Energy and Work

Energy and Work Energy and Work Physics Help Forum

Reply
 
LinkBack Thread Tools Display Modes
Old Sep 13th 2014, 08:05 AM   #1
Junior Member
 
Join Date: Sep 2014
Posts: 4
Bird dropping fish question

A sea bird catches a fish and then flies in an easterly direction with a speed v=7.39 m/s, h = 4.69 m above the surface of the sea. The fish has a mass of 115.3 g and is still alive. It thrashes and wiggles and as a result the bird drops the fish.

i) What is the speed of the fish when the bird drops it?

ii) What is the speed of the fish when it hits the water?

iii) When the fish hits the water it is momentarily stunned. It comes to a rest in 0.111 s. What is the magnitude of the force experienced by the fish as it comes to rest?

iv) How far horizontally from where it was dropped does the fish hit the water?

My attempt...

v^2 = u^2 +2gh
v2 ^2 = v2 ^2 + 2ad
s = ut + 0.5 x t^2
F = ma

i) What is the speed of the fish when the bird drops it?

Since v1 = 0
v2 ^2 = v1 ^2 + 2ad
v2 = √(2ad)
v2 = √(2 x 9.8 x 4.69)
v2 = 9.59 m/s

ii) What is the speed of the fish when it hits the water?
Using Pythagoras' Theorem,
a^2+ b^2 = c^2
∴ c = √(7.39^2 + 9.59^2)
c = 12.1 m/s

iii) When the fish hits the water it is momentarily stunned. It comes to a rest in 0.111 s. What is the magnitude of the force experienced by the fish as it comes to rest?
s = ut + 0.5 x t^2
4.69 = 0 + 0.5 x a x 0.111^2
a = 4.69 / (0.5 x 0.111^2)
a = 761.3 m/s^2
F = ma
F = 0.1153 x 761.3
F = 87.8 N

iv) How far horizontally from where it was dropped does the fish hit the water?

I can't seem to figure out a way to get this answer. Can someone please check if my answers are right and can give me an insight on how to answer this last question? Thank you!
HexyRexySmexy is offline   Reply With Quote
Old Sep 13th 2014, 11:25 AM   #2
Junior Member
 
Join Date: Sep 2014
Posts: 4
Nevermind about the first 3 questions. I ended up fixing them to the correct answers. However, I can't seem to figure out a way to get the last question. Does anyone have a way? Thanks
HexyRexySmexy is offline   Reply With Quote
Old Sep 13th 2014, 12:52 PM   #3
Junior Member
 
Join Date: Sep 2014
Posts: 4
Can someone quickly comment whether or not this is correct?

s = ut + 0.5 x t^2
s = (12.1 x 0.111) + 0.5 x (0.111)^2
s = 2.02 metres

Thanks!!
HexyRexySmexy is offline   Reply With Quote
Old Sep 13th 2014, 03:44 PM   #4
Physics Team
 
ChipB's Avatar
 
Join Date: Jun 2010
Location: Morristown, NJ USA
Posts: 2,321
For the last question the horizontal distance traveled before the fish hits the water is the horizontal velocity of the fish at release times the time it takes to fall to the water. That time is simply the time required for an object to drop 4.69m.
ChipB is offline   Reply With Quote
Old Sep 13th 2014, 10:26 PM   #5
Junior Member
 
Join Date: Sep 2014
Posts: 4
So, would the answer come from the distance over the speed found in (ii) 12.1 m/s to get the time, then multiplying that time by the initial horizontal speed to get the distance?

4.69 m / 12.1 m/s = 0.39 s
then to find the horizontal distance: 7.39 m/s x 0.39 = 2.86 m ?

Thanks again.
HexyRexySmexy is offline   Reply With Quote
Old Sep 14th 2014, 06:30 AM   #6
Physics Team
 
ChipB's Avatar
 
Join Date: Jun 2010
Location: Morristown, NJ USA
Posts: 2,321
That's not right - you are assuming that the rate of fall is constant, but it's not. The time it takes to fall is found from

s= (1/2)gt^2

Where h= 4.69m.
ChipB is offline   Reply With Quote
Reply

  Physics Help Forum > High School and Pre-University Physics Help > Energy and Work

Tags
bird, dropping, fish, question



Search tags for this page
Click on a term to search for related topics.
Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
An Archer Fish MarkL Kinematics and Dynamics 2 Jul 9th 2014 05:03 PM
Helicopter dropping a package mbruin Kinematics and Dynamics 2 Jun 26th 2014 10:34 PM
Bird feeder's force spartan301 Kinematics and Dynamics 6 Mar 27th 2011 06:15 PM
Bird-and-trains problem omirs Kinematics and Dynamics 2 Sep 26th 2010 07:13 PM
[SOLVED] Dropping problem xtheunknown0 Kinematics and Dynamics 2 Sep 16th 2010 01:38 AM


Facebook Twitter Google+ RSS Feed