On a dry road a car with good tires may be able to brake with an acceleration of 4.92 m/s². (a) How long does such a car, initially traveling at 24.6 m/s, take to come to rest? (b) How far does it travel in this time interval?
(a) The final velocity of the car when it comes to rest is zero. The initial velocity is 24.6 m/s and the acceleration is -4.92 m/s² (negative because it's the deceleration due to braking). We can use the formula:
v = u + at
where v is final velocity, u is initial velocity, a is acceleration, and t is time.
In this case, v = 0, u = 24.6 m/s, and a = -4.92 m/s². Plugging in these values, we get:
0 = 24.6 - 4.92t
Solving for t, we get:
t = 24.6/4.92
t ≈ 5 seconds
Therefore, the car takes about 5 seconds to come to rest.
(b) We can use the formula:
s = ut + 1/2 at²
where s is the distance traveled, u is the initial velocity, a is the acceleration, and t is the time.
In this case, u = 24.6 m/s, a = -4.92 m/s², and t = 5 seconds (which we just calculated). Plugging in these values, we get:
s = 24.6 × 5 + 1/2 × (-4.92) × 5²
s = 123 - 61.5
s = 61.5 meters
Therefore, the car travels about 61.5 meters during the 5 seconds it takes to come to rest.
Answers & Comments
Verified answer
Answer:
(a) The final velocity of the car when it comes to rest is zero. The initial velocity is 24.6 m/s and the acceleration is -4.92 m/s² (negative because it's the deceleration due to braking). We can use the formula:
v = u + at
where v is final velocity, u is initial velocity, a is acceleration, and t is time.
In this case, v = 0, u = 24.6 m/s, and a = -4.92 m/s². Plugging in these values, we get:
0 = 24.6 - 4.92t
Solving for t, we get:
t = 24.6/4.92
t ≈ 5 seconds
Therefore, the car takes about 5 seconds to come to rest.
(b) We can use the formula:
s = ut + 1/2 at²
where s is the distance traveled, u is the initial velocity, a is the acceleration, and t is the time.
In this case, u = 24.6 m/s, a = -4.92 m/s², and t = 5 seconds (which we just calculated). Plugging in these values, we get:
s = 24.6 × 5 + 1/2 × (-4.92) × 5²
s = 123 - 61.5
s = 61.5 meters
Therefore, the car travels about 61.5 meters during the 5 seconds it takes to come to rest.