Force
What is a force? (not the formula)
a push or a pull
What is work?
The force needed to displace a mass
What is Momentum? And why is it a vector quantity?
Force in the movement of an object
It is a vector quantity because it is described by its magnitude and velocity.
What is mechanical power?
The energy needed to do work
OR
the rate at which work is done
Usain Bolt and a sumo wrestler are running up the stairs. Usain Bolt gets to the top in half the time as the sumo wrestler. Who has the most power?
Not possible to answer unless you know each of their masses.
What is the acceleration of an object that is pushed with 12N and has a mass of 3kg?
12N/3kg = 4N/kg or 4m/s2
A teacher applies a force to a wall and becomes exhausted. Is this work?
Nothing is moving, so no work.
Determine the momentum of a 1000-kg car moving northward at 20 m/s.
Momentum = mass x velocity
p = 1000kg x 20m/s = 20,000kgm/s
James does 1000J of work in 200 seconds. How much power is he using?
Power = work/time
1000J/200s = 5watts = 5W
A 5000kg truck is at a stop light waiting for the light to turn green, and the engine is running. How much momentum does the truck have?
0 momentum, as it is not moving
A force of 15N is applied onto a book, causing it to accelerate at 5m/s2. What is the mass of the book?
15N/5m/s2 = 3kg
A boy lifts a 30N dragon 2 meters above the ground. How much work did the boy do on the dragon?
work = force x displacement
30N x 2meter = 60Joules
A car possesses 20 000 units of momentum. What would be the car's new momentum if its velocity was doubled?
use a number to represent velocity and mass, so 10m/s and 2000kg
momentum before = 20,000kgm/s =2000kg x 10m/s
momentum after = 2000kg x 20m/s =
40,000kgm/s
So the momentum doubles.
Two physics students, Will and Ben, are in the weightlifting room. Will lifts the 100-kg barbell 1 meter, 5 times in 50s; Ben lifts the 100-kg barbell 1 meter, 10 times in 100 seconds. Which student uses the most power? (use 10m/s2 as the acceleration of gravity, and count only the work to lift, not to bring the weight down.)
Will's work = 1000N x 5m = 5000J
Will's power = 5000J / 50s = 100W
Ben's work = 1000N x 10m = 10,000J
Ben's power = 10,000J / 100s = 100W
Power is equal.
I can jump about 6 times higher on the moon than on Earth. I can jump about 3 times higher on Mars. Why?
The acceleration of gravity on the moon is about 1/6 of Earth and on Mars, about 1/3 of Earth.
Suppose that a sled is accelerating at a rate of 2 m/s2. If the net force is tripled and the mass is doubled, then what is the new acceleration of the sled?
Answer: 3 m/s/s
The original value of 2 m/s/s must be multiplied by 3 (since a and F are directly proportional) and divided by 2 (since a and m are inversely proportional)
If you are in a car that is being pulled along a 50.0 m path with a force of 10 Newton’s (N), what is the “work” done on the car?
Work = force x displacement
J = 10N x 50m = 500 J
Two trains are attaching themselves to each other at a station. Train A has a mass of 10000 kg and is travelling at a velocity of 3 m/s, it combines with a stationary train B with a mass of 5000 kg. What is the final velocity of the combined trains?
total momentum before = total momentum after
Momentum train = 10,000kg x 3m/s = 30,000kgm/s
Momentum train B = 0, total momentum 30,000kgm/s, (total mass, 15,000kg)
Momentum after = 30,000kgm/s
30,000kgm/s = 15,000kg x ?
velocity = 2m/s
When doing a chin-up, a physics student lifts her 40kg body a distance of 0.25 meters in 2 seconds. What is the power delivered by the student's biceps?
Power = force x distance / time
400N x 0.25 = 100J
100J / 2 s = 50W
Who won the Nobel Prize this year for Medicine/Physiology?
Svante Pääbo
Suppose that a sled is accelerating at a rate of 2 m/s2. If the net force is tripled and the mass is halved, then what is the new acceleration of the sled?
Answer: 12 m/s/s
The original value of 2 m/s/s must be multiplied by 3 (since a and F are directly proportional) and divided by 1/2 (since a and m are inversely proportional)
A crane does work of 10,000 J with a force of 5000 N to lift a beam. How far can the beam be lifted (in meters)?
work = force x displacement
10,000J = 5000N x ?
2 meters
Jenny is standing on ice holding a bowling ball, she weighs 50 kg and the ball 10 kg. With what velocity must she throw the ball so that she moves backwards with a velocity of 2 m/s?
picture answer
Why is power a scalar quality?
It has no direction, just a quantity.
What is Sora's last name? (spelling matters)
Ramnebro