Chapter 1 Kinematics Essay

Chapter 1 Kinematics

Subchapter – Kinematics

1. A car is driving at a constant speed of 40 m/s (almost 90 mph) on a highway. It passes a stationary police car on the side of the road. The police car begins to chase the speeding car with a constant acceleration of 4 m/s2. How long will it take for the officer to catch up with the speeding car? 20 seconds 10 seconds The police car never catches up 4.47 seconds

Correct Answer – A 20 seconds

Explanation:

A: The police car catches up with the speeder when their positions (their x values) are the same. We don’t need to know what the value of x is, just that they are the same.

Using the equation x= x_i+ v_i t+ 1/2 at^2for both the speeder and police car we can solve for time by setting the speeder’s

Steve throws a 15 pound shot straight up into the air, giving it a constant acceleration of 42 m/s2 for 55 centimeters. He releases it 2.1 meters above the ground. Ignoring air resistance and assuming the shot started at rest, How much time does Steve have to move before the shot hits his head (he is 1.85 meters tall)? 13.9 seconds 1.39 seconds 23.1 seconds 1.42 seconds

Correct Answer – D 1.42 seconds

Explanation:

Note: You may be tempted to convert the pounds to kilograms, but don’t. The weight is a red herring and isn’t used in the problem.

A: This answer came from not converting the 55 centimeters to meters.

B: While this answer may look like dividing answer A by 10, it actually came from finding out how long it would take the ball to return to 2.1 meters high.

C: This answer comes from multiplying the acceleration by the distance the shot was in Steve’s hand.

D: To calculate how long he has to get out of the way, the velocity the shot leaves his hand must be calculated first using v_f^2= v_i^2+2a(x_f- x_i ) where vi = 0 m/s, a = 42 m/s2 and (xf – xi) = 0.55 m. the velocity when the shot leaves his hand is 6.8 meters per second.

We calculate the time before the shot will hit his head using x_f- x_i= v_i t+ 1/2 at^2 where xf = 1.85 m, xi = 2.1 m, vi = 6.8 m/s and a = -9.8 m/s2. Subchapter Free