physics

What is the acceleration of a car that maintains a constant velocity of 100 km/hr for 10 seconds?

0

The average speed of a horse that gallops a distance of 10 kilometers in a time of 30 minutes is

Convert time to hours: 30 min = 0.5 h Then, v = d / t = 10 km / 0.5 h = 20 kph

If a projectile is fired straight up at a speed of 10 m/s, the total time to return to its starting position is about

Let up be positive. vo = 10 m/s, a = g = -9.8 m/s², t = ? Symmetrical, so vf = - vo t = (vf - vo)/ t = (10 m/s - (-10 m/s)) / -9.8 m/s² = 2.04 s ≈ 2 s

A man leans over the edge of a cliff and throws a rock upward at 4.9 m/s. How far below the level from which it was thrown is the rock 2 seconds later?

Let up be positive. vo = 4.9 m/s, a = g = -9.8 m/s², t = 2 s, d = ? d = vo t + ½ g t² = (4.9 m/s)(2 s) + ½ (- 9,8 m/s²)(2 s)² = - 9.8 m The negative sign tells you it is below the starting point.

A ball tossed vertically upward rises, reaches its highest point, and then falls back to its starting point. During this time the acceleration of the ball is always

directed downward.

Galileo's use of inclined planes allowed him to effectively

slow down the acceleration of free fall.

A car accelerates uniformly. It starts from rest and reaches 36 m/s after 6.0 seconds. During the 6.0 seconds it has traveled _______________ m.

vavg = (vo + vf) / 2 = (0 + 36 m/s) / 2 = 18 m/s d= vavg t = (18 m/s)(6 s) = 108 m

If a rocket initially at rest accelerates at a rate of 50 m/s² for one minute, its speed will be

vo = 0; a 50 m/s², t = 1 min = 60 s vf = vo + g t = 0 + (50 m/s²)(60 s) = 3000 m/s

It takes 6 seconds for a stone to fall to the bottom of a mine shaft. How deep is the shaft?

vo = 0; a = g (down positive), t = 6 s d = vo t + ½ g t2 = 0 + ½ (9.8 m/s²)(6 s)² = 17604 m ≈ 180 m

Ten seconds after starting from rest, an object falling freely downward will have a speed of about

vo = 0; a = g (let downward be positive), t = 10 s vf = vo + g t = 0 + (9.8 m/s²)(10 s) = 98 m/s ≈ 100 m/s

A car moving initially at 30 m/s comes gradually to a stop in 900 m. What was the acceleration of the car?

vo = 0; vf = 30 m/s; d = 900 m No time given, so use vf2 = vo2 + 2 a d a = (vf2 - vo2 ) / 2 d = (0 - (30 m/s)²) / (2)(900 m) = -0.5 ms/²

An auto, starting from rest, undergoes constant acceleration and covers a distance of 1250 meters. The final speed of the auto is 50 meters/sec. How long does it take the car to cover the 1250 meters?

vo = 0; vf = 50 m/s; d = 1250 m; t = ? vavg = (vo + vf) / e2 = (0 + 50 m/s) / 2 = 25 m/s d = vavg t → t = d / vavg = 1250 m / 25 m/s = 50 s