A skateboarder goes off a horizontal ledge a short distance above the sidewalk.

The skateboarder has a horizontal velocity of 7.0 m/s and the ledge is 55 cm above the ground.

Find: (a) How far from a point directly below the edge of the ledge does the skateboard touch down? [2.3 m](b) What are the horizontal and vertical components of the skateboard when it hits the sidewalk? [7.0 m/s , 3.28 m/s]

2-21 (Sister)

As a car approaches an intersection, the green light turns yellow. The driver unwisely decides to accelerate and is able to just barely enter the intersection before the light turns red.

At a time of 3.0 s before the light turns red, the car is 51 m from the intersection and its speed is 14 m/s.

Find: (a) What is the car’s speed when it enters the intersection? [20 m/s] (b) What is the acceleration of the car? [2 m/s/s]

3-D1 (Some numbers borrowed from 3-B6)

Assuming the car in the above problem continues to accelerate before the driver suddenly discovers the need for a panic stop.

The car has a mass of 1,000 kg and, in a full skid, experiences a force of 3,000 N. It is going at a speed of 21 m/s when the brakes are applied and reaches a fender bending speed of 2 m/s after some distance.

Find: (a) What is the negative acceleration of the car? [3 m/s/s] (b) What is that distance? [72 m]

3-B26
(Substantially revised.) Inspired by an amusement park ride called the Tidal Wave, some neighbor kids decide to set up a miniature version with a baby stroller accelerated by the weight of a cement block tied to a rope passing over a pulley.

The baby stroller with occupant has a mass of 120 kg while the cement block has a mass of 40 kg. The cement block can travel a distance 2.5 m before hitting the ground.

Find: (a) Assuming very little friction, what is the acceleration of the baby stroller? [2.5 m/s/s] (b) What is the speed of the cement block when it hits the ground? [3.5 m/s] (c) What is the tension in the rope while the system is accelerating? [294 N]

4-D1 (Similar to the lawn mower example we talked about in class.)

A lame old man is leaning on his shopping cart while pushing it at constant velocity toward the produce section of the supermarket.

He pushes on it with a force of 150 N directed 75^o below the horizontal. The fully loaded shopping cart weighs 200 N.

Find: (a) How great is the frictional force acting on the cart? [39 N] (b) How great is the total downward force acting on the cart? [345 N] (c) Calculate the value of the appropriate coefficient of friction. [0.112]

4-C10 (With some numbers changed and parts added.)

A 10kg cake of ice starting from rest slides down a chute that is 6.7 m long and inclined 30^o to the horizontal. The ice reaches the bottom of the chute with a speed of 7.6 m/s.

Find: (a) What is the unbalanced force acting on the ice cake in the direction in which it is accelerating? [43 N](b) How great is the normal force acting between the ice and the chute? [85 N](c) Calculate the value of the appropriate coefficient of friction.[0.069]