Question

Need help on these two questions on my math review.

A car moving with a speed of 108 km/h is brought to rest in a distance of 60 m. How much time did the car take to stop?

2 seconds

4 seconds

6 seconds

8 seconds

An object is thrown with an initial velocity of 3 m/s. What is its acceleration at its maximum height?

zero

3 m/s2

-9.8 m/s2

none of the above

Answer 1

can we assume constant acceleration?

Answer 2

or deceleration in this instance

Answer 3

yes?

Answer 4

there are equations we can use
x = 1/2 * a * t^2 + v*t
v^2 = u^2 + 2*a*s

Answer 5

1 km = 1000 m
1 m = 1/1000 km

v^2 = u^2 + 2*a*s
60 m = 60* 1/1000 km
0^2 = 108^2 + 2*a*60*1/1000

a = -108^2 / ( 2 * 60 /1000 )

Answer 6

a = -97200

now plug this into
v = u + a*t

0 = 108 + (-97200) * t

-108 / -97200 = t
note that time is in hours
to get seconds multiply by 3600

Answer 7

The next question, the acceleration due to gravity is always -9.8 , near the surface of earth.

Answer 8

-9.8 m/s^2