Physics 50 Sample Midterm Exam #1 (26 points) by Todd Sauke
Question #1.
A train starts from rest (at initial position = 0) and accelerates uniformly, until it has traveled 3.3 km and acquired a velocity of 48 m/s. The train then moves at a constant velocity of 48 m/s for 430 s. The train then decelerates uniformly at 0.065 m/s2 until it is brought to a halt. We want to determine the acceleration during the first 3.3 km of travel. Fill in the table below with the values of the kinematic variables for the problem involving the first 3.3 km of travel. Write "target" in the table to indicate the target variable.
| x| x0| vx| v0x| ax| t|
1 point
Write the constant-acceleration equation (from the study guide) involving the given kinematic variables and the target variable.
______
1 point
Solve the equation for the target variable. (Make sure to use SI units consistently)
acceleration= ______
1 pointinclude units (½ point)
How much farther does the train travel during the 430 s of constant velocity motion?
______
1 point (units) ½ point
Now we want to determine the total distance traveled by the train once it has stopped moving. Fill in the table below with the values of the kinematic variables for the problem involving the final (decelerated) travel. Write "target" in the table to indicate the target variable.
| x| x0| vx| v0x| ax| t|
1 point
What is the total distance traveled by the train?______
1 point (include units to get full credit)
Question #2.
A racquetball strikes a wall with a speed of 30 m/s and rebounds with a speed of 26 m/s. The collision takes 20 ms (milliseconds). We want to determine the magnitude of the average acceleration of the ball during the collision.
Write the equation (from the study guide) for finding the average acceleration.
______
1 point
What is the magnitude of the average acceleration of the ball during the collision?
______
2 pointsinclude units to get full credit
Question #3.
A projectile is fired at time t = 0.0s, from point 0 at the edge of a cliff, with initial velocity components of v0x = 80 m/s and v0y = 600 m/s The projectile rises, then falls into the sea at point P, as shown in the figure. The time of flight of the projectile is 150.0 s. We want to determine the magnitude of the velocity of the projectile at time t = 15.0 s (in mid-flight). Remember that for projectile motion, the x and y motions are independent, with y acceleration given by gravity and x acceleration zero. First let's figure out the vertical velocity of the projectile at t = 15.0 s. Fill in the table below with the values of the y-axis (vertical) kinematic variables relevant to the problem. Write "target" in the table to indicate the target variable.
| y| y0| vy| v0y| ay| t|
1 point
Write the equation involving the appropriate kinematic variables.
______
1 point
Solve for the vertical velocity of the projectile at t = 15.0 s. vy(15) = ______m/s
1 point
What is the horizontal velocity of the projectile at t = 15.0 s? vx(15) = ______m/s
1 point
What is the magnitude of the velocity of the projectile at time t = 15.0 s? ______m/s
1 point
Question #4.
A plastic ball in a liquid is acted upon by its weight and by a buoyant force. The weight of the ball is 2.7 N. The buoyant force has a magnitude of 7.1 N and acts vertically upward. At a given instant, the ball is released from rest. We want to determine the acceleration of the ball at that instant, (including direction). Make a free body diagram of the ball, including all of the things that should be in a good free body diagram.
Write the equation for determining the
acceleration of the ball when released.
______
1 point
What is the acceleration of the ball?
______m/s2
Free body diagram, 2 points1 point
Question #5.
A block is on a horizontal frictionless table, on earth. The block accelerates at 8.4 m/s2 when a 90 N horizontal force is applied to it. Now the block and table are set up on the moon. The acceleration due to gravity at the surface of the moon is 1.62 m/s2. A horizontal force of 45 N is applied to the block when it is on the moon. We want to determine the acceleration imparted to the block. Make a free body diagram of the block when it is on earth, including all of the things that should be in a good free body diagram.
Write the equation relating the horizontal
acceleration, mass and forces on the block
when it is on the earth.
______
½ point
What is the mass of the block?
______kg
Free body diagram (earth), 1 point1 point
Make a free body diagram of the block when it is on the moon, including all of the things that should be in a good free body diagram.
Write the equation relating the horizontal
acceleration, mass and forces on the block
when it is on the moon.
______
½ point
What is the acceleration of the block?
______m/s2
Free body diagram (moon), 1 point1 point
Question 6. (2 points)
Two football teams, the Raiders and the Jets, are engaged in a tug-of-war. The Raiders are pulling with a force of 5,000 N. Which of the following is an accurate statement?
A) The Jets are pulling with a force of more than 5,000 N if they are winning, i.e. pulling the Raiders in the direction toward the Mets.
B) The Jets are pulling with a force of 5,000 N.
C) The tension in the rope is 10,000 N.
D) The tension in the rope depends on whether or not the teams are in equilibrium.
E) None of these statements is true.