For (c), at max height, v=0, so use v2 = u2 + 2as, just put u=20, a=-9.81, s=54

In summary: For (c), at max height v=0, then v=u + at, then a=-9.81.In summary, the man throws a stone with an initial speed of 20 m/s vertically upward from a building with a height of 54 m. It takes 2.04 seconds to reach a velocity of 40 m/s and the velocity before it reaches the ground is approximately 4 m/s. The magnitude of its acceleration at its maximum height is 9.8 m/s^2.
  • #1
madinsane
32
0

Homework Statement



a man throws a stone vertically upward with initial speed of 20 m/s from a building with height 54 m a)how long does the stone take to reach 40 m/s
b)what is its velocity before it reaches the ground
c) what is the magnitude of its acceleration at its maximum height?


Homework Equations


vf=vi+at
xf=xi+vit+0.5at
vf^2=vi^2+2a(xf-xi)

The Attempt at a Solution


I just want someone to tell me whether what I have done is right or wrong
so for a)
I took vi=20m/s
vf=0m/s (I was going to calculate how long it takes to reach the maximum peak)
then I used vf=vi+at (a as-9.8)
I got 2.04 s
Then I took vi=0
vf=40
then used the same thing and got t as ~4 and then I added them together
b) At first I calculated the distance it takes to go from the building to the peak
using xf=xi+vit+0.5at
xi=0
vi=20
t=2.04
a=-9.8
I got ~22m
Then I added to the 54
then I used vf^2=vi^2+2a(xf-xi)
vi=0
a=-9.8
xf=76
xi=0
and got vfinal
c) I said it was 9.8 m/s^2
So did I do anything wrong and if I did tell me what it is
 
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  • #2
You're correct, but it can be done simpler
For (a), v = u + at, just put v=-40, u=20, a=-9.81
For (b), v2 = u2 + 2as, just put u=20, a=-9.81, s=-54
 

What is projectile motion in physics?

Projectile motion in physics refers to the motion of an object that is launched into the air and then moves along a curved path under the influence of gravity.

What are the key factors that affect projectile motion?

The key factors that affect projectile motion are the initial velocity, the angle of launch, and the force of gravity.

What are the two components of projectile motion?

The two components of projectile motion are the horizontal and vertical components. The horizontal component is constant, while the vertical component is affected by gravity.

How does the angle of launch affect projectile motion?

The angle of launch affects the range and height of the projectile. The maximum range is achieved when the angle of launch is 45 degrees.

What is the formula for calculating the range of a projectile?

The formula for calculating the range of a projectile is R = (v2 * sin(2θ)) / g, where R is the range, v is the initial velocity, θ is the angle of launch, and g is the acceleration due to gravity.

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