How Do You Calculate Initial Speed in Projectile Motion Problems?

AI Thread Summary
To calculate initial speed in projectile motion, one must consider both horizontal and vertical components of motion. In the first problem, a ball thrown horizontally from 22 m hits the ground with a speed three times its initial speed, while the second problem involves a projectile fired at a 30° angle from 41 m, striking the ground at 1.4 times its initial speed. The user attempted to apply the kinematic equation V^2=Vo^2+2ah but encountered errors, suggesting the need for a clearer understanding of vertical acceleration. It is emphasized that only the vertical component of motion is subject to acceleration due to gravity. Clarifying the calculations and focusing on the vertical motion will lead to the correct initial speed.
heeling23
Messages
1
Reaction score
0
1. A ball is thrown horizontally from a height of 22 m and hits the ground with a speed that is three times its initial speed. What was the initial speed?

2. A projectile is fired with initial speed v at an angle 30° above the horizontal from a height of 41 m above the ground. The projectile strikes the ground with a speed of 1.4v. Find v.

These are essentially the same problems right? Except for the fact that #2 has a vertical initial velocity. I tried using V^2=Vo^2+2ah but I got the answer wrong. Then I tried finding the time for the first one using y=1/2at^2 and then using v=vo+at and I got the wrong answer again.

Any help is appreciated!
Thanks,
heeling23
 
Physics news on Phys.org
heeling23 said:
I tried using V^2=Vo^2+2ah but I got the answer wrong. Then I tried finding the time for the first one using y=1/2at^2 and then using v=vo+at and I got the wrong answer again.
Either approach, done correctly, would work. Post the details of what you did for more help. (Hint: Only the vertical component of motion is accelerated.)
 

Thread 'Struggling to understand the concept of this question (ice cube in water optics question)'

TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
View full post »
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

Find the height of a lamp based on the velocities of projectiles
Replies
40
Views
2K
How Do You Solve a Projectile Motion Problem?
Replies
3
Views
4K
A ball is thrown w/initial speed vi at an angle 𝜃i with the horizontal
Replies
5
Views
1K
Projectile Motion Problem Involving Initial Velocity and Gravity Only
Replies
11
Views
1K
Projectile motion with ##N## bounces on the ground
Replies
21
Views
1K
Projectile Motion -- Help please understanding these basic problems
Replies
4
Views
1K
Projectile Motion of motorcyclist
Replies
20
Views
3K
Find Projectile Flight Time Given Only Maximum Height
Replies
4
Views
2K
In the horizontal direction, what is the initial velocity of the projectile?
Replies
1
Views
1K
How Does Projectile Angle Affect Asymptotic Behavior in Physics Graphs?
Replies
23
Views
3K

Hot Threads

Recent Insights

Back
Top