Momentum Basics
What is the formula for momentum?
p = mv (momentum = mass × velocity)
What is the formula for impulse?
J = Ft (impulse = force × time)
In a car crash, why are airbags useful in terms of impulse?
Airbags increase the time of impact, reducing the force experienced by passengers.
A 2 kg ball is moving at 3 m/s. What is its momentum?
6 kg·m/s
What happens to the momentum of an object if its velocity doubles?
The momentum doubles.
If a car has a mass of 1000 kg and is moving at 20 m/s, what is its momentum?
20,000 kg·m/s
How is impulse related to change in momentum?
Impulse is equal to the change in momentum (J = Δp).
What is conserved in an isolated system where no external forces act?
Momentum is conserved.
A force of 15 N is applied to an object for 3 seconds. What is the impulse?
45 N·s or 45 kg·m/s
Can an object have momentum without having kinetic energy? Explain.
No, because momentum depends on velocity and mass, and kinetic energy depends on the square of velocity. If there’s momentum, there’s kinetic energy.
True or False: Momentum is a scalar quantity.
False (Momentum is a vector quantity)
True or False: Impulse has the same units as momentum.
True (both are measured in kg·m/s)
How does a rocket change its momentum in space?
By expelling gas out of its engines (conservation of momentum).
A 10 kg object initially at rest is subjected to an impulse of 50 N·s. What is its final velocity?
5 m/s
Describe a real-life situation where impulse is applied to reduce injury.
Wearing seatbelts in a car; they stretch slightly to increase the time over which the force acts, reducing the force.
What are the units of momentum?
kg·m/s
What is the impulse experienced by a 5 kg object subjected to a 10 N force for 2 seconds?
20 N·s or 20 kg·m/s
Why do athletes follow through when hitting a ball?
To increase the time of contact, thereby increasing the impulse and the change in momentum of the ball.
Two ice skaters push off each other and move in opposite directions. Skater A (50 kg) moves at 2 m/s. What is the momentum of skater B (70 kg)?
-100 kg·m/s (opposite direction, so negative sign)
Why does a heavy truck require more force to stop than a small car, if both are traveling at the same speed?
Because the truck has more momentum due to its greater mass.
If two objects have the same momentum, what can be said about their mass and velocity?
The product of mass and velocity is the same for both objects, but they may have different masses and velocities.
If the time of impact is increased, what happens to the force experienced by an object?
The force decreases (for the same impulse).
In a collision, how is it possible for two objects to have different forces acting on them yet the same impulse?
They experience the same impulse because impulse depends on the change in momentum, but the forces can differ due to different contact times.
A 0.5 kg ball moving at 10 m/s strikes a wall and bounces back at 5 m/s. What is the change in momentum?
-7.5 kg·m/s
How does the conservation of momentum explain the recoil of a gun when it is fired?
The momentum of the bullet forward is equal and opposite to the momentum of the gun backward, conserving momentum in the system.