Title: Pre-Unit Assessment
Course: MNPCC Physics > Section: Newton's Third Law

This assessment will only be used to gauge your understanding of the concepts heading into the unit.

Q: A child is pulling a wagon.  The force on the child and the force on the wagon are shown here.  In which direction will the child and wagon accelerate?

Wagon and Girl by openclipart / Public Domain
- Additional forces must be shared in order to answer this. (Correct)
- The two forces balance out so there will be no acceleration. (The forces can't cancel as they are on two different objects.)
- The wagon will accelerate forwards and the girl will accelerate backwards. (They are attached and must have the same acceleration.)
A: Additional forces must be shared in order to answer this.
If right: Your answer is correct.
If wrong: Your answer is incorrect.

Q: A bat strikes a ball pitched at 90 mph.  How does the force on the bat compare to the force on the ball?
- The force from the ball on the bat and the force from the bat on the ball are equal. (Correct)
- The force of the ball on the bat is greater than the force of the bat on the ball. (They are equal.)
- The force of the ball on the bat is less than the force of the bat on the ball. (They are equal.)
A: The force from the ball on the bat and the force from the bat on the ball are equal.
If right: Your answer is correct.
If wrong: Your answer is incorrect.

Q: A father and daughter are ice skating.  From a stand still the 100 kg father pushes off on his 25 kg daughter.  How do their accelerations compare?
- The daughter accelerates more. (Correct.)
- The accelerations are equal. (The forces are equal, but the masses are different.)
- The father accelerates more. (Acceleration is inversely proportional to mass. And force is the same.)
A: The daughter accelerates more.
If right: Your answer is correct.
If wrong: Your answer is incorrect.

Q: How does the force needed to bring an object to a halt depend on the time that it takes to do it?
- The longer the time, the less force is needed. (Correct.)
- The time has no bearing on the force required. (The time impacts the acceleration.)
- The longer the time, the greater the force. (The opposite is true.)
A: The longer the time, the less force is needed.
If right: Your answer is correct.
If wrong: Your answer is incorrect.

Q: Which object will be harder to be brought to a stop.  A 0.1 kg ball moving at 10 m/s or a 1 kg ball moving at 1 m/s?
- It will be equally difficult to stop them both. (Correct.)
- The more massive ball will be more difficult to stop. (Both mass and speed matter.)
- The faster moving ball will be more difficult to stop. (Both mass and speed matter.)
A: It will be equally difficult to stop them both.
If right: Your answer is correct.
If wrong: Your answer is incorrect.

Q: A semi-truck rear ends a car.  Assuming no other forces such as breaking, which of the following is true.
- The semi will slow down more than the car speeds up. (The semi has more mass.)
- The car will speed up more than the semi slows down. (Correct.)
- The amount the semi slows down is equal to the amount the car speeds up. (The semi has more mass.)
A: The car will speed up more than the semi slows down.
If right: Your answer is correct.
If wrong: Your answer is incorrect.

Q: Two identical wagons are being pulled with identical force.  For wagon A the force is applied for 10 seconds and for wagon B the force is being applied for 20 seconds.  Which wagon will have the highest final speed?
- Wagon B. (Correct)
- Wagon A (Wagon B has the force applied for more time.)
- The final speed will be identical. (Wagon B has the force applied for more time.)
A: Wagon B.
If right: Your answer is correct.
If wrong: Your answer is incorrect.

Q: A sailboat has a powerful fan directly behind and all air from the fan is blown directly into the sail.  What will happen to the motion of the boat?
- The boat's motion will remain constant. (Correct.)
- The boat will speed up as air is forced into the sail. (This is balanced by the backwards force on the fan, forces must be external to change motion.)
- The boat will slow down as the fan is pushing it backwards. (This is countered by the force on the sail. You need external forces to change the motion of a system.)
A: The boat's motion will remain constant.
If right: Your answer is correct.
If wrong: Your answer is incorrect.

Q: A rocket works because...
- As it pushes gas out the back, the gas pushes back on the rocket. (Correct.)
- The gas that is pushed out of the rocket pushes on the gas already present around it. (Then how does a rocket work in space?)
- The gas that is pushed out pushes against the ground. (Then the force would decrease with altitude, of what if the rocket isn't pointed at the ground?)
A: As it pushes gas out the back, the gas pushes back on the rocket.
If right: Your answer is correct.
If wrong: Your answer is incorrect.

Q: A student sits on a chair.  What is the reaction force to the chair pushing up on the student?
- The student pushing down on the chair. (Correct.)
- The student pulling up on the chair. (Right object, wrong direction.)
- The Earth pulling down on the student. (These forces are equal and opposite, but are not action/reaction pairs.)
- The student pulling up on the Earth. (Wrong system to be a reaction pair.)
A: The student pushing down on the chair.
If right: Your answer is correct.
If wrong: Your answer is incorrect.