Question

Which of the following decreases in motion along a straight line with constant retardation?

• A. speed
• B. acceleration
• C. displacement
• D. none of these

Answer 1

The correct option is A speed

• Option A:

By first equation of motion,

$v=u-at$

Since it is retardation, then $a\to negative$

Let us assume the moving body has some initial speed $u$ in $+x$ axis.

So we can see, as time $t$ increases, final speed $v$ decreases.

So option A is correct.

• Option B:

Acceleration can't decrease because it is given in the question itself that it is constant retardation, i.e, constant acceleration opposite in direction to the speed.

• Option C:

Displacement will also keep on increasing towards $+x$ axis as long as final speed $v$ doesn't become zero.