Homework answers / question archive / 2

2

Physics

Share With

2.42 A brick is dropped (zero initial speed) from the roof of a building. The brick strikes the ground in 1.90 s. You may ignore air resistance, so the brick is in free fall. (a) How tall, in meters, is the building? (b) What is the magnitude of the brick’s velocity just before it reaches the ground? (c) Sketch a_y-t, u_y-t, and y-t graphs for the motion of the brick.

2.36 A small rock is thrown vertically upward with a speed of 22.0m/s from the edge of the roof of a 30.0-m-tall building. The rock doesn’t hit the building on its way back down and lands on the street below. Ignore air resistance. (a) What is the speed of the rock just before it hits the street? (b) How much time elapses from when the rock is thrown until it hits the street?

2.34 At the instant the traffic light turns green, a car that has been waiting at an intersection starts ahead with a constant acceleration of 2.80 m/s². At the same instant a truck, traveling with a constant speed of 20.0 m/s, overtakes and passes the car. (a) How far beyond its starting point does the car overtake the truck’

(b) How fast is the car traveling when it overtakes the truck?

(c) Sketch an x-t graph of the motion of both vehicles. Take x = 0 at the intersection.

(d) Sketch a v_x-t graph of the motion of both vehicles.

2.18 CALC The position of the front bumper of a test car under microprocessor control is given by x(t) = 2.17 m + (4.80 m/s²)t² — (0.100 m/s⁶)t⁶.

(a) Find its position and acceleration at the instants when the car has zero velocity.

(b) Draw x-t, U_x - t, and a_x-t graphs for the motion of the bumper between t = 0 and t = 2.00s.

2.21 A Fast Pitch. The fastest measured pitched baseball left the pitcher’s hand at a speed of 45.0 m/s. If the pitcher was in contact with the ball over a distance of 1.50 m and produced constant acceleration, (a) what acceleration did he give the ball, and (b) how much time did it take him to pitch it?