OO mobily 11:15 PM docs.google.com 2a CALE A car is stopped at a traffic light.

Question

OO mobily 11:15 PM docs.google.com 2a CALE A car is stopped at a traffic light. It then travels along a straight road such that its distance from the light is given by x() br cr., where b 240 m/s and c o 120 m/s (a) Calculate the average velocity of the car for the time interval 0 to r 100 Calculate the instantaneous velocity of the car att 50s, and 00s How long after starting from rest is the car again at rest? 2.8 CALC A bird is flying due east. Its distance fromatallbuild- What is the instantaneous velocity of the bird when t 800s? 2.14 CALC A race car starts from rest and travels east along a straight and level track. For the first 50s of the car's motion. the eastward component of the car's velocity is given by we() (0860 m/s )r. What is the acceleration of the car when 12.0 m/s? 2.15 CALCA turtle crawls along a straight line, which we will call the A-axis with the positive direction to the right. The equa- ion for the turtle's position as a function of time is x(r 50 o em (2.00 cm/s)r (0.0625 cm/s )r. Ga Find the turtle's nitial velocity, initial position, and initial what time is the velocity of the turtle zero? How long after 2.22 A Tennis Serve. n the fastest measured tennis serve, the ball left the racquet at 7.I4m/s. A served tennis ball is cally in contact with the racquet for 300 ms and starts from rest Assume constant acceleration Ca What was the balls during this serve?(b0 How far did the ball travel daring the serve? Aut omobile Air Bags. The human body can sur- vive an acceleration trauma incident esudden stop) if the magni tude of the acceleration is less than 250 m/s. If you are in an automobile accident with an initial speed of 105 km/h(65mih) and are stopped by an airbag that inflates from the dashboard. over what distance must the airbag stop you for you to survive 2.36 A small rock is thrown vertically upward with a speed of 220 m/s from the edge of the roof of a 300-m-tall building The rock doesn't hit the building on its way back down and lands en the street below. Ignore air resistance, a What is the speed of the rock just before it hits the street?(bR How much time elapses from when the rock is thrown until it hits the street? 2.37 A juggler throws a bowling pinstraight up with an initial speed of 820 m/s. How much time elapses until the bowling pin returns to the iuggler's hand? 31%

Explanation / Answer

2.14.

I think we are meant to understand that the rate of change of acceleration during 5s is 0.860m/s³ and that initial acceleration and speed are both zero.

Then a = acceleration = du/dt = 1.72 × t
When u =12.30m/s ; t² = 12.0/0.86 = 13.953 s; giving t = 3.735 s
and a = 1.72 × 3.735 = 6.424 m/s

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