Physics Unit 1 Quiz

How much air resistance acts on a freely falling object?

None! "Freely falling" means the only force acting on the object is gravity.

A ball is tossed into the air: What is its acceleration when it's moving up? What is its acceleration when it reaches maximum height? What is its acceleration when it's moving down?

The acceleration due to gravity is always -10 m/s^2.

A ball is dropped off of a tall building and falls for 6 seconds. Does the ball fall further in the first 3-second interval, the second 3-second interval, or is the distance the same?

The ball falls further in the second 3-second interval. As a ball falls, it speeds up. Therefore, it travels a greater distance with each second.

If you simultaneously drop a book and a flat sheet of paper, the ________________ will hit the ground first. Why?

The book will hit the ground first. The sheet of paper is slowed down by air resistance (due to both its area and light weight).

What happens when a car's velocity and acceleration are in opposite directions?

The car slows down.

What happens when a car's velocity and acceleration are in the same direction?

The car speeds up.

Instead of dropping a ball, you throw a ball directly downward. How does this affect the ball's velocity and acceleration?

Throwing the ball would give it an initial velocity which would increase its overall velocity when compared to a ball that was dropped from rest. However, the acceleration due to gravity is always -10 m/s^2.

How do we solve right angle velocity vector problems?

We must use the Pythagorean Theorem to find the length of the hypotenuse - which is the Resultant. R = square root(A^2 + B^2)

A biker increased his velocity from 2 m/s to 8 m/s in 3 seconds moving in a straight line. What is the acceleration of the biker?

a = (final velocity-initial velocity)/time a = (8 m/s - 2 m/s)/3 s = 2 m/s^2

vector quantity

a quantity that has both magnitude and direction examples: velocity (55 miles per hour north) acceleration (10 m/s^2 downward)

scalar quantity

a quantity that has magnitude only (but no direction) example: speed (55 miles per hour)

Galileo discovered that when air resistance can be neglected, all objects fall with the same ______.

acceleration

Velocity-Time graphs tell us an object's

acceleration. (Why? Because acceleration is defined as change in velocity/change in time.)

If you simultaneously drop a book and a crumpled ball of paper, they will ___________________ . Why?

hit the ground at the same time Crumpling the paper reduces the paper's surface area - making air resistance negligible.

speed

how fast an object covers a distance; how fast an object moves speed = distance/time unit is m/s scalar quantity (magnitude only)

velocity

how fast and in what direction an object changes position velocity = distance/time + direction (Velocity is speed + direction!) unit m/s vector quantity

A speedometer measures

instantaneous speed.

speed formula

speed = distance/time

When an object is in free fall...

the only force acting on it is gravity.

acceleration

the rate of change in velocity a = (final velocity-initial velocity)/time unit m/s^2 vector quantity (both magnitude and direction)

free fall formulas

to find an object's position in free fall: d = 1/2at^2 to find an object's velocity in free fall: v = initial velocity + at Note: Oftentimes, initial velocity is zero, so you may see the formula: v = at

What is the speed of an object in free fall 4 seconds after being dropped from a rest position?

v = at v = 10 m/s^2 * 4 s = 40 m/s

right angle velocity vector example What is the speed of an airplane flying at 100 km/hr caught in 100 km/hr right angle crosswind?

v = square root(100^2 + 100^2) = 141 km/hr

A car traveling along an oval track at 45 km/h is moving with constant speed but not constant ______________ . Why?

velocity The car's velocity (speed plus direction) is NOT constant because on an oval track, the direction is changing.

velocity formula

velocity = (x-final - x-initial)/time or velocity = change in position/change in time

Position-Time graphs tell us an object's

velocity.

A car is traveling eastward, and for every second it travels, the car covers less distance. What is the direction of the car's acceleration vector?

westward (Why? If the car is covering less distance, then it's slowing down. Since the velocity is eastward, the acceleration must be westward.)

Acceleration due to gravity (g) is ALWAYS

-10 m/s^2 or 10 m/s^2 downward

A car is moving at a constant velocity of 24 m/s east for 20 seconds. What is its acceleration?

0 m/s (Why? Because acceleration is defined as a change in velocity per unit time. This car has a constant velocity (constant speed and constant direction), so it is NOT accelerating.

A ball is tossed upward. What is the magnitude of its acceleration at the top of its ascent?

10 m/s^2

What is your average speed when you drive 150 kilometers in 3 hours?

150 km/3 h = 50 km/h

You are on a bus that is traveling 35 miles per hour (mph). You walk from the front of the bus to the back at 4 mph. What is your speed relative to the road outside?

35 mph - 4 mph = 31 mph

You are on a bus that is traveling 50 miles per hour (mph). You walk from the back of the bus to the front at 5 mph. What is your speed relative to the road outside?

50 mph + 5 mph = 55 mph

How does air resistance affect the acceleration of a falling object?

Air resistance decreases the acceleration of falling objects. (Note, the object is falling, NOT free falling.)

When an object is freely falling, how much speed does it gain each second?

It gains 10 m/s of speed each second it falls.

When a ball is dropped downward, with each second what happens to its speed, acceleration, and distance traveled?

It gains 10 m/s of speed each second. It's acceleration is always -10 m/s^2. It travels more distance each second.

When a ball is tossed upward, with each second what happens to its speed, acceleration, and distance traveled?

It slows down, losing 10 m/s of speed each second. It's acceleration is always -10 m/s^2. It covers less distance each second.

If a car is moving 65 mph due west, is it accelerating?

No! Acceleration is defined as the change in velocity per unit time. This car has a constant speed and a constant direction, so it is NOT accelerating.

When is an object accelerating?

An object accelerates when it increases speed or velocity. An object accelerates when it decreases speed or velocity. An object accelerates when it changes direction.

A ball is tossed into the air. What is its speed when it's moving up? What is its speed when it reaches maximum height? What is its speed when it's moving down?

As it moves upward, it loses 10 m/s of speed each second. At maximum height, its speed = zero. As it falls, it gains 10 m/s of speed each second.

How far do you travel moving at 60 mph for 20 mins?

Check to match sure the units match! 20 mins = 1/3 hour "How far..." means you're solving for distance. Re-arrange the speed formula: d = st d = 60 mph (1/3 h) = 20 miles