Kinematic Equations

An apple drops from a tree and hits the ground at a speed of 16 m/s. How long did it take to fall?

• 1.6 s

• -1.6 s

• 157 s

• -157 s

Answer explanation

Did you make the 16m/s negative? It is moving in the downward direction.

Remember that time cannot ever be negative, it is a scalar.

Did you chose the vf = ... equation?

Tags

NGSS.HS-PS2-1

NGSS.HS-PS2-4

An apple drops from a tree and hits the ground at a speed of 16 m/s. What is its displacement?

• -13 m

• +13 m

• +157 m

• -157 m

Answer explanation

Since the apple was moving downward, it's displacement is negative.

Did you use the vf^2=... equation?

Tags

NGSS.HS-PS2-4

Kenny Klutz throws his physics book straight up into the air with a speed of 3.2 m/s. How high up in the air will it go?

• 0.522 m

• 31.36 m

• 3.06 m

• 0.327m

Answer explanation

Since time is not given and not the unknown, choose the equation that does not have a t in it.

vf^2 = ....

Tags

NGSS.HS-PS2-1

Mars has an acceleration due to gravity of -3.47 m/s². How far will a quarter dropped from rest on Mars fall in 1.5 s?

Ignore air resistance.

• 11 m

• 3.9 m

• 5.2 m

• 2.31 m

Answer explanation

Did you use Mars' gravity instead of 9.8?

Since the questions asked how far it fell, the answer does not require as (-) sign.

Did you use the x = vit.... equation?

Tags

NGSS.HS-PS2-1

NGSS.HS-PS2-4

On earth, what speed will a quarter dropped from rest acquire in 1.5 s?

• 14.7 m/s

• 9.8 m/s

• 6.5 m/s

• 11 m/s

Answer explanation

Since the question asked for speed, there is no need to give a negative answer as speed is a scalar.

Did you choose the vf=... equation?

Tags

NGSS.HS-PS2-1

You drop your pencil from your desk and it hits the floor 0.45 seconds later. How many meters tall is the desk?

Give your answer with 2 decimal places. Do not include the unit.

Mathematical Equivalence

ON

Answer explanation

Since it asked how tall your desk is, you want to give a positive number.

Did you use the x = vit... equation?

Tags

NGSS.HS-PS2-1

NGSS.HS-PS2-4

On the moon, a freely falling object has an acceleration of due to gravity of -1.6 m/s². If you were to drop a penny on the moon, what would its displacement be after 1.8 s?

• -2.59 m

• +2.59 m

• -2.88 m

• +0.89 m

Answer explanation

Since the penny is falling and it asks for displacement, your answer should be negative.

Did you use the x = vit... equation?

Tags

NGSS.HS-PS2-1

If an object is falling from rest on the earth, what two pieces of information are given?

• acceleration and final velocity are positive

• final velocity is 0 m/s

• acceleration is -9.8 m/s^2

• initial velocity is 0 m/s

Tags

NGSS.HS-PS2-4

If an object is thrown straight up in the air on the earth, what two pieces of information are given?

• acceleration and initial velocity are negative

• initial velocity is 0 m/s

• acceleration is -9.8 m/s^2

• final velocity at the top of its path is 0 m/s

Answer explanation

The initial velocity is a positive number. This is the speed at which the object leaves your hand or whatever launched it up. It cannot be zero as it wouldn't go up if you released it from rest.

Tags

NGSS.HS-PS2-4

Why is it important for us to have several kinematic equations?

• The knowns vary

• The unknowns vary

• The goals of a question vary

• All of the above