A1150 kg pile driver is used to drive a steel i-beam into the ground. the pile driver falls 7.69 m before contacting the beam, and it drives the beam 7.76 cm into the ground before coming to rest. find the magnitude of the average force the beam exerts on the pile driver while the pile driver is brought to rest.

the average force 11226 N  

Explanation:

Let's analyze the problem we are asked for the average force, during the crash, we can find this from the impulse-momentum equation, but this equation needs the speeds and times of the crash that we could look for by kinematics.

Let's start looking for the stack speeds, it has a free fall, from rest  (Vo=0)

           Vf² = Vo² - 2gY

            Vf² = 0 - 2 9.8 7.69 = 150.7

            Vf = 12.3 m / s

This is the speed that the battery likes when it touches the beam.  They also give us the distance it travels before stopping, let's calculate the time

            Vf = Vo - g t

             0 = Vo - g t

             t = Vo / g

             t = 12.3 / 9.8

             t = 1.26 s

This is the time to stop

Now let's use the equation that relates the impulse to the amount of movement

                 I = Δp

                F t = pf-po

The amount of final movement is zero because the system stops

                F = - po / t

                F = - mv / t

                F = - 1150 12.3 / 1.26

                F = -11226 N

This is the average force exerted by the stack on the vean

the minimum constant speed at which she can catch the train is 2.7 m/s

given:

acceleration = 0.6

time = 4.5 s

to find:

velocity = ?

formula used:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

solution:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

v = 0 + (0.6 × 4.5)

v = 2.7 m/s

the minimum constant speed at which she can catch the train is 2.7 m/s