<h2>
Mass of object in Earth is 1.37 kg</h2>
Explanation:
On planet B where the magnitude of the free-fall acceleration is 1.91g , the object weighs 25.74 N.
We have
Weight = Mass x Acceleration due to gravity
On planet B
25.74 = Mass x 1.91 g
25.74 = Mass x 1.91 x 9.81
Mass = 1.37 kg
Mass is constant for an object. It will not change with location.
Mass of object in Earth = Mass of object in Planet B
Mass of object in Earth = 1.37 kg
Work = Force x displacement
Force= 20N
Displacement= 0.75m
W= 20(0.75)
W= 15 Nm
Slope of a curve Y plotted against X is mathematically given as

now here we can see that if similarly graph is plotted against distance and time then slope is given as

here we can say that above is ratio of small distance and very small interval of time.
so here we can say that this ratio of distance and time for very small interval of time is known as instantaneous speed of the object which is falling freely under gravity.
So here slope of the graph will represent the speed at a given instant.
Answer:
because there is many places for it to bounce of of creating another soundwave