A20-kg barrel is rolled up a 20-m ramp to the back of a truck whose floor is 5.0 m above the ground. what work is done in loading one barrel into the truck?

The angle of inclination is calculated using sin function,

sin θ = 5 m / 20 m = 0.25

θ = 14.4775° 

The net force exerted is then calculated:
F net = m g sin θ = 20 * 9.8 * 0.25

F net = 49N 

Work is product of net force and distance:
W = F net * d = 49 * 20

Work = 980 J 

diagram is missing, but i will try to explain your doubt.

answer:

amplitude is the maximum displacement or distance moved on a point of a vibrating body or wave measured from its equilibrium position.it is equal to half the length of vibration path.