Resultant velocity practice problems
1. Ann is at the airport and is in a rush. She normally travels north at 2 m/s. If she gets
on a “moving sidewalk “ that travels at 2 m/s north and walks on it, what will be her
resultant velocity?
Ann = 2m/s north
Sidewalk = 2 m/s north
They are the same direction so you add velocities.
2 m/s + 2m/s = 4m/s North
2. Ann is still traveling north in the airport. She has two choices, take a place and stand
on a north moving sidewalk at 2 m/s or to walk north at 3m/s on the empty south
“moving sidewalk” that travels at 2m/s? Which choice is faster?
North sidewalk
Ann= 0 m/s
Sidewalk = 2 m/s north
0 + 2m/s = 2m/s north
South sidewalk Ann =
3m/s north Sidewalk =
2 m/s south
They are in opposite directions so you subtract velocities
3m/s north – 2m/s south = 1 m/s north
Standing on the north sidewalk is faster
3. An action hero is running on top of a train traveling at 55m/s. If our hero is moving
toward the front of the train at a speed of 5 m/s, what is our hero’s resultant velocity?
Train = 55 m/s forward
Hero = 5 m/s forward
The directions are the same so this is an addition problem
55m/s =+ 5 m/s = 60 m/s forward.
4. You are on a bus traveling 47 m/s forward. You go to the back of the bus to visit your
friend you are walking at a speed of 3 m/s. What is your resultant velocity?
Bus = 47 m/s forward
You = 3m/s to the back
Your directions are opposite so you subtract
47m/s- 3m/s = 44m/s forward
Acceleration problemsThe formula for acceleration is (final velocity – starting velocity)/ time
1. A race car is traveling 150 m/s north. 30 seconds later the car is traveling 200 m/s.
what is the acceleration of the race car?
Starting velocity = 150 m/s North
Final velocity = 200m/s north
Time = 30 s
(final velocity – starting velocity)/ time
(200m/s – 150m/s) / 30 s
( 50 m/s) / 30 m/s
Velocity = 1.67 m/s/s north
2. The race car traveling at 300 m/s west slows down to a stop in 120 seconds. What is
the acceleration of the race car?
Starting velocity= 300m/s west
Final velocity = 0 m/s ( stop)
Time = 120 seconds
(final velocity – starting velocity)/ time
(0m/s- 300m/s) / 120 s
( - 300m/s) /120s
-2.5 m/s/s west ( Negative acceleration means slowing down or stopping)
3. You take a shopping cart that is not moving and race it down the grocery isle at 10 m/s
in 3 seconds. What is your acceleration?
Starting velocity = 0 m/s
Final velocity = 10 m/s
Time = 3 s
(final velocity – starting velocity)/ time
(10m/s – 0 m/s) / 3
10 m/s / 3s
3.33 m/s/s forward ( if no direction is given the direction is forward)
4. You are riding your bike down the bike path at 10 m/s When you come up to a hill
that speeds you up to 15 m/s as you go down it. If the hill takes 13 s to go down what is
you acceleration?
Starting velocity = 10 m/s
Final velocity= 15 m/s
Time= 13 s
(final velocity – starting velocity)/ time
( 15m/s – 10 m/s) / 13s
(5 m/s) / 13 s
0.38 m/s/s forward
5. You are riding you bike north at a constant speed of 5 m/s. What is your acceleration?
Starting velocity= 5 m/s
Final velocity = 5 m/s
Time – not given
(final velocity – starting velocity)/ time
5-5 = 0 you can’t divide into 0 so even if a time was given the answer is that this is not
acceleration
6. A lion runs eastward at a velocity of 30 m/s. two seconds later, it tackles it’s prey to
the ground. What is the lion’s acceleration?
Starting velocity = 30 m/s
Final velocity = 0m/s ( to the ground indicates it is no longer moving)
Time = 2s
(final velocity – starting velocity)/ time
( 0m/s-30 m/s)/ 2 s
( - 30 m/s) / 2 s
- 15 m/s/s forward Make sure you r answer is negative!
Net force questions
1. Two forces are acting on an object one has a magnitude of 12 N and is directed to the
north. The other has a magnitude of 7 N and is directed to the south. The object
experiences a net force of ….
Force 1 = 12 N north
Force 2 = 7 N south
Opposite directions is subtraction
12 N north – 7N south = 5 N north
2. What is the net force of when you combine a force of 15 N north and 12 N north?
Force 1= 15 N north
Force 2 = 12 N north
Both forces are in the same direction so you add them
15N north + 12 N north = 27 N north
3. What is the net force when you combine a force of 15 N north with a force of 12 N
south?
Force 1 = 15 N North
Force 2 = 12 N south
Forces are in opposite directions so you subtract them
15 N North- 12 N south = 3 N North
4. Two dogs are playing tug of war. The big dog exerts a force of 8N. The smaller dog
exerts a force of 4 N. Who wins the tug and by how much?
Big dog = 8 N
Small dog = 4 N
Tug of war means opposite directions which is subtraction
8N ( big dog ) – 4 N small dog = 4 N big dog wins