Is it possible that a ball is thrown downward/upward with zero initial velocity? [closed]

Question

• The way I've seen the motion of a ball thrown vertically:

All balls are thrown with an initial speed. In my understanding, it's not possible that something goes either upward or downward with nonzero velocity.

When thrown upward: the initial velocity a ball is thrown with is the maximum velocity of the motion and the velocity diwndles as the ball approaches the maximum height. When it reaches the maximum height, velocity is zero.

When thrown downward: again, the initial velocity a ball is thrown with is the maximum velocity of the motion and the velocity diwndles as the ball approaches the ground. When it touches, velocity is zero.

• The type of questions that was thus understandable to me:

I just started working on different questions about motion along a straight line (acceleration is constant). All the problems related to throwing a ball vertically I've faced gave intial velocity that is not zero. For example, "A ball is thrown down vertically with an initial speed of v₀=10m/s from a height of h=15.0m". Then it would usually ask how long the ball takes to reach the ground or the final speed when it touches the ground. I was able to solve this kind of questions.

• A question that didn't make sense to me:

Full question: "A device for measuring your reaction time consists of a cardboard strip marked with a scale and two large dots. A friend holds the strip vertically, with thumb and forefinger at the dot on the right. You then position your thumb and forefinger at the other dot, being careful not to touch the strip. Your friend releases the strip, and you try to pinch it as soon as possible after you see it begin to fall. The mark at the place where you pinch the strip gives your reaction time." And then it asked the usual question about displacement: "How far from the lower dot should you place the 50.0ms mark?"

So the only information I received was t=50.0ms and a=9.8m/s^2. No information about velocity is given. The only formulas I've learned in this chapter are the following five, and everything must be solvable with these:

v=v₀+at

x-x₀=v₀t+$\frac{1}{2}$a$t^2$

$v^2$=$v₀^2$+2a(x-x₀)

x-x₀=$\frac{1}{2}$(v₀+v)t

x-x₀=vt-$\frac{1}{2}$a$t^2$

But since I only have two quantities x-x₀ and a, I wasn't able to solve the question on my own and referred to the answer key. The answer key was suggesting the second formula I presented above: Δy=v₀t+$\frac{1}{2}$a$t^2$

Then it wrote Δy=$\frac{1}{2}$g$t^2$ considering v₀ as zero. I wasn't able to understand that the cardboard was thrown with no initial velocity.

• Is it ever possible that a ball in a general setting is thrown upward or downward with no initial velocity? If it's possible, what happens? If it's not possible, is the answer key wrong? Or does it imply different type of understanding?

Answer 1

I think you misunderstand the distinction between 'throw' and 'drop'. When you throw something, you apply a force to it, so both it and your hand are moving when you release it from your grip. When you drop something, you release it from your grip without first having accelerated it, so it does start with zero velocity (more or less).