When unbalanced force is acting on the system of mass then as per Newton's II law we can say

here we have

now since the force and mass both given to us so we can find acceleration of object from this
now when 50 N force is applied on a box then this 50 N force is unbalanced force on it and it will produce acceleration to the box
So here we can say that box will accelerate with constant acceleration and hence its velocity will linearly increase with time.
Now the displacement of the object will be given as

so here the displacement will be a quadratic function of time and increases with time as well
so here overall the motion will be of constant acceleration, uniformly increasing velocity and displacement will be a quadratic function of time
If gold gets hot enough, and melts, then this is a <u>physical change</u><u>.</u>
Melting is a physical change. Keep in mind that temperature and melting are both physical properties.
The diagram is missing; however, we know that the intensity of a sound wave is inversely proportional to the square of the distance from the source:

where I is the intensity and r is the distance from the source.
We can assume for instance that the initial distance from the source is r=1 m, so that we put

The intensity at r=3 m will be

Therefore, the sound intensity has decreased by a factor

.
The correct choice is
D. 22 Hz and 42 Hz.
In fact, the beat frequency is given by the difference between the frequencies of the two waves:

In this problem, the beat frequency is
, therefore the only pair of frequencies that gives a difference equal to 20 Hz is
D. 22 Hz and 42 Hz.