Physics Test

The first half of upward motion has a positive ___________ and a negative ____________

Initial velocity, acceleration (gravity)

Upward motion is symmetrical. Explain what that means.

It means: distance traveled up = distance traveled down, time to get to the top = time to get back down, speed at a given height going up = speed at same height going down

Object A has a mass of 10kg Object B has a mass of 50kg If we drop both A and B from the same height at the same time, which will hit the ground first?

They will hit the ground at the same time because the acceleration due to gravity (little g) does not change when mass changes.

The two metal balls of the previous problem roll off a horizontal table with the same speed. In this situation:

both balls hit the floor at approximately the same horizontal distance from the base of the table.

You throw a ball vertically upward. Which statement best describes the direction and magnitude of the ball's velocity while the ball is still moving up?

upward, decreasing magnitude

What is the acceleration of objects free falling?

-10 m/s^2 Remember the negative means direction. Gravity points down (and is causing the acceleration) so the acceleration is negative.

You throw a ball vertically upward. Which statement best describes the direction and magnitude of the ball's acceleration while the ball is still moving up?

...

A ball is launched vertically upward from ground level with an initial velocity of 30 m/s. What maximum altitude does it reach above the ground? Use |g|=10 m/s2.

45 m

A ball is launched vertically upward from ground level with an initial velocity of 30 m/s. How much time does it take before it lands on the ground? Use |g|=10 m/s2.

6 s

Free fall motion is...

Falling caused by gravity, with nothing else effecting it (no air resistance)

At the very top of upward motion, what does the object do as it changes from moving upward to moving downward?

It stops!

During our lab work and demonstrations, did we use true "free fall" motion? Stick to the definition.

No! In class we always have to deal with air, which we ignore for free fall motion.

An object moving upward in the air is ___________ because gravity is pulling in the opposite direction.

Slowing down!

Two metal balls are the same size but one weighs twice as much as the other. The balls are dropped from the roof of a single story building at the same instant of time. The time it takes the balls to reach the ground below will be

about the same for both balls.

A boy throws a steel ball straight up. Consider the motion of the ball only after it has left the boy's hand but before it touches the ground, and assume that forces exerted by the air are negligible. For these conditions, the force(s) acting on the ball is (are):

an almost constant downward force of gravity only.

A stone dropped from the roof of a single story building to the surface of the earth

speeds up because of an almost constant force of gravity acting upon it