Answer:
Explanation:
When the spring is compressed by .80 m , restoring force by spring on block
= 130 x .80
= 104 N , acting away from wall
External force = 82 N , acting towards wall
Force of friction acting towards wall = μmg
= .4 x 4 x 9.8
= 15.68 N
Net force away from wall
= 104 -15.68 - 82
= 6.32 N
Acceleration
= 6.32 / 4
= 1.58 m / s²
It will be away from wall
Energy released by compressed spring = 1/2 k x²
= .5 x 130 x .8²
= 41.6 J
Energy lost in friction
= μmg x .8
= .4 x 4 x 9.8 x .8
= 12.544 J
Energy available to block
= 41.6 - 12.544 J
= 29 J
Kinetic energy of block = 29
1/2 x 4 x v² = 29
v = 3.8 m / s
This will b speed of block as soon as spring relaxes. (x = 0 )
B. picking up a box off the floor
Answer:
momentum =0
kinetic energy >0, positive
Explanation:
The final momentum is zero but the final kinetic energy is positive.
The momentum is zero because momentum is the sum of the mass×velocity for each component. momentum is conserved
The KE is positive because KE is the sum of the 1/2×mass×velocity^2.
Whereas velocity can be positive and negative since it is (it's what makes the momentum zero because on is positive and one is negative), the velocity squared will always be positive.
Adding together two positives will always be a positive number.
