91Ó°ÊÓ

A block is given an initial speed of 4.5 m/s up a 22.0° plane, as shown in Fig. 4–59. (a) How far up the plane will it go? (b) How much time elapses before it returns to its starting point? Ignore the friction.

The crate shown in Fig. 4–60 lies on a plane tilted at an angle $\mathrm{θ}=\mathbf{25}\mathbf{.}{\mathbf{0}}^{\mathbf{o}}$to the horizontal, with ${\mathrm{μ}}_{\mathrm{k}}=0.19$. (a) Determine the acceleration of the crate as it slides down the plane. (b) If the crate starts from rest 8.15 m up along the plane from its base, what will be the crate’s speed when it reaches the bottom of the incline?

FIGURE 4–60 Crate on inclined plane. Problems 59 and 60

A person stands on a scale in an elevator. His apparent weight will be the greatest when the elevator

(a) is standing still.

(b) is moving upward at a constant velocity.

(c) is accelerating upward.

(d) is moving downward at a constant velocity.

(e) is accelerating downward.

A person has a reasonable chance of surviving an automobile crash if the deceleration is no more than 30 g’s. Calculate the force on a 65-kg person accelerating at this rate. What distance is traveled if brought to rest at this rate from$95\mathrm{km}/\mathrm{h}$.

When a golf ball is dropped to the pavement, it bounces back up. (a) Is a force needed to make it bounce back up? (b) If so, what exerts the force?

(II) A crate is given an initial speed of 3.0 m/s up the 25.0° plane shown in Fig. 4–60. (a) How far up the plane will it go? (b) How much time elapses before it returns to its starting point? Assume${\mathrm{μ}}_{\mathrm{k}}=0.2$.

FIGURE 4–60Crate on inclined plane. Problems 59 and 60.

(II) A car can decelerate at$-\mathbf{3}.\mathbf{80}\mathrm{m}/{\mathrm{s}}^2$without skidding when coming to rest on a level road. What would its deceleration be if the road is inclined at 9.3° and the car moves uphill? Assume the same static friction coefficient.

A skier moves down a 12° slope at constant speed. What can you say about the coefficient of friction,${\mathrm{μ}}_{\mathrm{k}}$? Assume the speed is low enough that air resistance can be ignored.

The coefficient of kinetic friction for a 22-kg bobsled on a track is 0.10. What force is required to push it down along a 6.0° incline and achieve a speed of 60 km/h at the end of 75 m?

On an icy day, you worry about parking your car in your driveway, which has an incline of 12°. Your neighbor’s driveway has an incline of 9.0°, and the driveway across the street is at 6.0°. The coefficient of static friction between tire rubber and ice is 0.15. Which driveway(s) will be safe to park in?