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Projectile motion ball throw problem

  • #1

Homework Statement


A ball is thrown upwards from the top of a building with an initial velocity of 20 m/s and at an angle of 30 (degrees) with the horizontal. The height of the building from the ground level is 25m. Determine (i) where and when it will strike the ground (ii) velocity with which it strikes the ground (iii)maximum height reached by the ball above the ground level.

Homework Equations


T total = (2Vi sin(theta))/2(9.81)
Range, R= (Vi)^2 sin2(theta)/ (9.81)


The Attempt at a Solution


i have solve for Vx= 20cos30 = 17.32 m/s
Vy=20sin30= 10 m/s
 

Answers and Replies

  • #2
Redbelly98
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Homework Statement


A ball is thrown upwards from the top of a building with an initial velocity of 20 m/s and at an angle of 30 (degrees) with the horizontal. The height of the building from the ground level is 25m. Determine (i) where and when it will strike the ground (ii) velocity with which it strikes the ground (iii)maximum height reached by the ball above the ground level.

Homework Equations


T total = (2Vi sin(theta))/2(9.81)
Range, R= (Vi)^2 sin2(theta)/ (9.81)
There are 4 or 5 equations relevant to projectile motion, and they should all be in your textbook.

There are problems with the two equations you list here. The first equation should contain initial and final velocities, but only has the initial velocity. Also, that range equation is only valid for the projectiles launched from ground level -- not the case here.

The Attempt at a Solution


i have solve for Vx= 20cos30 = 17.32 m/s
Vy=20sin30= 10 m/s
[/QUOTE]
I would start by finding how long it takes the ball to hit the ground. Check out the equations for projectile motion, and see which can be used to find time t given the information you know about height, initial velocity, and acceleration in the y (vertical) direction.
 

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