MCAT Physical : MCAT Physical Sciences
Study concepts, example questions & explanations for MCAT Physical
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Example Questions
Example Question #1 : Biochemistry, Organic Chemistry, And Other Concepts
A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
How would the voltaic cell depicted above differ from an electrolytic cell?
An electrolytic cell requires energy input
An electrolytic cell produces more energy, but only after an input of energy to begin the process
An electrolytic cell produces energy based on differences in concentrations between the half cells
An voltaic cell requires energy input to begin the reduction process
An electrolytic cell produces more energy
An electrolytic cell requires energy input
Electrolytic cells require an input of energy, and are used to plate metals by functionally running a voltaic cell in reverse.
Example Question #1 : Electrochemistry
Which of the following is not true of electrolytic cells?
The cell potential is negative
Electrons travel toward the cathode
Electricity is conducted by the motion of ions
Oxidation occurs at the anode
No battery is required for electrolysis to take place
No battery is required for electrolysis to take place
For electrolytic cells, the cell potential is negative; in contrast, galvanic/voltaic cells have positive cell potentials. Electrolysis reactions can only occur if the total potential is positive. An additional voltage input, such as a battery, is required so that the sum of potentials in the electrolytic cell is greater than zero.
Oxidation always occurs at the anode, regardless of cell type, and electrons always travel toward the site of reduction (the cathode). In a galvanic cell, the cathode is positively charged, naturally drawing the flow of electrons. In an electrolytic cell, the cathode is negatively charged, but still requires the flow of electrons to allow reduction to occur. An induced current from a battery is used to propel these electrons against their natural flow.
Example Question #4 : Electrochemistry
Which of the following is true about electrolysis?
I. It only involves reactions with
II. It requires a voltage source
III. It is an exothermic process
II only
I only
I and II
II and III
II only
Electrolysis is a specific type of reaction that occurs in an electrolytic cell. An electrochemical cell contains an anode and a cathode that facilitate a redox reaction. In an electrolytic cell (a type of electrochemical cell) the redox reaction that is carried out is a nonspontaneous reaction. Recall that the change in Gibbs free energy for a nonspontaneous, or unfavorable, reaction is always positive; therefore, for electrolysis in an electrolytic cell, the redox reaction has a 
Nonspontaneous reactions are reactions that are unfavorable. This means that energy is required to carry out the reaction. In an electrolytic cell, energy is provided in the form of voltage input. The voltage provided pushes the reaction in the unfavorable direction; therefore, electrolysis reactions require a voltage source. Statement II is true.
Since it requires energy, an electrolysis reaction is considered to be an endothermic process. Recall that endothermic processes are reactions that take in (or require) energy, whereas exothermic processes are reactions that release energy; therefore, electrolysis is an endothermic process. Statement III is false.
Example Question #5 : Electrochemistry
Consider the following reaction:
How much voltage will you have to apply to carry out this reaction?
Less than
No voltage needs to be applied because this reaction represents a galvanic cell
Greater than
No voltage needs to be applied because this reaction represents an electrolytic cell
Greater than
The question states that the reaction has a negative 
In an electrolytic cell, energy is provided by an external voltage source. Without energy, the electrolytic cell will have a voltage of 
Example Question #1 : Newtonian Mechanics And Motion
A 200-gram object moves in the +x direction at 4m/s and collides with an identical object moving in the –y direction at 3m/s. If the two objects stick together after the collision, what is the magnitude of their resulting velocity?
3.5m/s
5m/s
7m/s
2.5m/s
6.5m/s
2.5m/s
Use conservation of momentum in each direction: 
The initial momentum in the x direction is provided only by the first object.
This also equals the final x-momentum, when the two objects move together at the same velocity.
The initial momentum in the y direction is provided only by the second object.
Again, this equals the final y-momentum.
Combine the two velocities using the Pythagorean theorem.
Example Question #2 : Newtonian Mechanics And Motion
Two children are playing with sleds on a snow-covered hill. Sam weighs 50kg, and his sled weighs 10kg. Sally weighs 40kg, and her sled weighs 12kg. When they arrive, they climb up the hill using boots. Halfway up the 50-meter hill, Sally slips and rolls back down to the bottom. Sam continues climbing, and eventually Sally joins him at the top.
They then decide to sled down the hill, but disagree about who will go first.
Scenario 1:
Sam goes down the hill first, claiming that he will reach a higher velocity. If Sally had gone first, Sam says they could collide.
Scenario 2:
Sally goes down the hill first, claiming that she will experience lower friction and thus reach a higher velocity. If Sam had gone first, Sally says they could collide.
Scenario 3:
Unable to agree, Sam and Sally tether themselves with a rope and go down together.
If the hill is frictionless, what momentum does Sam experience when he reaches the bottom of the 50m hill on his sled in Scenario 1?
1340kg*m/s
0kg*m/s
1898kg*m/s
1581kg*m/s
60kg*m/s
1898kg*m/s
The momentum is equal to Sam's total mass times his velocity. His velocity can be found from his potential energy, using conservation of energy. Keep in mind, his total mass includes the mass of his sled.
PE = mgh = (50kg + 10kg) * 10m/s2 * 50m
PE = 30,000J
KE = 30,000J = 1/2mv2 = 1/2(60kg)(v2)
v2 = 1000 m2/s2 = 31.2m/s
p = mv = 60 kg * 31.2 m/s = 1898 kg*m/s
If you had used 30J in place of 30kJ in the KE calculation, you would have chosen 60kg*m/s
Example Question #1 : Newtonian Mechanics And Motion
Two children are playing with sleds on a snow-covered hill. Sam weighs 50kg, and his sled weighs 10kg. Sally weighs 40kg, and her sled weighs 12kg. When they arrive, they climb up the hill using boots. Halfway up the 50-meter hill, Sally slips and rolls back down to the bottom. Sam continues climbing, and eventually Sally joins him at the top.
They then decide to sled down the hill, but disagree about who will go first.
Scenario 1:
Sam goes down the hill first, claiming that he will reach a higher velocity. If Sally had gone first, Sam says they could collide.
Scenario 2:
Sally goes down the hill first, claiming that she will experience lower friction and thus reach a higher velocity. If Sam had gone first, Sally says they could collide.
Scenario 3:
Unable to agree, Sam and Sally tether themselves with a rope and go down together.
A third boy, John, comes to play on a neighboring hill. Sally goes to play with him, and they find that after they sled down the first hill, Sally was traveling 12m/s. John was only moving at 8m/s. John weighs 80kg with his sled. Which of the following is true?
Sall has greater momentum, John has greater kinetic energy
Sally has lower momentum, John has lower kinetic energy
Sally has greater momentum, while they have roughly equal kinetic energies
Sally has lower momentum, John has greater kinetic energy
Sally has greater momentum, John has lower kinetic energy
Sally has lower momentum, John has lower kinetic energy
Kinetic energy emphasizes velocity, by squaring the velocity term.
KE = 1/2mv2
Sally's KE = 1/2(52 kg)(12 m/s)2 = 3,744J
John's KE = 1/2(80 kg)(8m/s)2 = 2,560J
p = mv
Sally's Momentum = 52kg * 12m/s = 624 kg*m/s
John's Momentum = 80kg * 8m/s = 640 kg*m/s
Example Question #1 : Newtonian Mechanics And Motion
Two astronauts, Ann and Bob, conduct a collision experiment in a weightless, frictionless environment. Initially Ann moves to the right with a momentum of 
Apply conservation of momentum before and after the collision.
Taking left to be the negative direction, and noting that Bob's initial momentum is 0 since he is at rest, we can use the provided information to see that 
Solving for 
Example Question #1 : Translational Motion
In a totally inelastic collision between two objects, all of the following are true, except that __________.
the two objects stick together
kinetic energy is conserved
momentum is conserved
energy is conserved
kinetic energy is conserved
The difference between an elastic and inelastic collision is that in an elastic collision BOTH momentum and kinetic energy are conserved. Momentum is conserved in any collision, but when a collision is inelastic, kinetic energy is dissipated when the two individual objects combine. This energy can be in the form of heat, explosion, sound, etc. In a totally inelastic collision, the two objects colliding stick together and travel with the same velocity in one direction.
Overall energy is conserved, as the energy is merely transferred from a kinetic form to a non-kinetic form.
Example Question #6 : Newtonian Mechanics And Motion
Which object has the most momentum?
I. A 
II. A 
III. An 
I
I, II, and III are equal
III
II
II and III are equal
III
We can find the momentum for each object using the momentum formula, 
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