Aforce of 8 lb is required to hold a spring stretched 8 in. beyond its natural length. how much work w is done in stretching it from its natural length to 14 in. beyond its natural length?

work done=-8.166lb-ft

Explanation:

force = 8 lb       spring stretched (x)= 8 in

according to hooks law

F=-kx

k=-

k=-

k=-1 lb/in

work done=

work done=

work done=-98lb-in

1 ft =12 in

work done=

                 =-8.166lb-ft

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