- #1

- 169

- 0

Thank you!

A.

## Homework Statement

A rolling ball moves from x1=3.4 cm to x2=-4.2 cm during the time from t1=3.0 s to t2=6.1 s. What is the average velocity?

## Homework Equations

and## The Attempt at a Solution

Average velocity = (x2 - x1)/(t2-t1) ~ (-2.5 cm/s)

B.

## Homework Statement

A sports car accelerates from rest to 95 km/h in 6.2 s. What is the average acceleration in m/s^2?

## Homework Equations

and## The Attempt at a Solution

average acceleration = (v2 - v1)/(t2-t1) ~4.3 m/s^2.

C.

## Homework Statement

At highway speeds, a particular automobile is capable of an acceleration of about 1.6 m/s^2. At this rate, how long does it take to accelerate from 80km/h to 110 km/h?

## Homework Equations

and## The Attempt at a Solution

v1= 80 km/h = 22 m/s

v2= 110 km/h = 31 m/s

Average acceleration = 1.6m/s^2=(v2 - v1)/(∆t)=> it takes 5.6 seconds.

D.

## Homework Statement

A horse canters away from its traiener in a straight line, moving 116m away in 14.0 seconds. It then turns abruptly and gallops halfway back in 4.8 seconds. Calculate its average speed and its average velocity for the entire trip, using away from the trainer as the positive direction.

## Homework Equations

and## The Attempt at a Solution

Average speed=d/t=(116 + 58)/(14.0 + 4.8 seconds) = 9.3 m/s.

Average velocity= ∆x/∆t=3.1m/s.

E.

## Homework Statement

A light plane nust reach a speed of 33m/s for takeoff. How long a runway is needed if the constant acceleration is 3.0 m/s^2?

## Homework Equations

and## The Attempt at a Solution

(x-xo) = (v^2 -vo^2)/2a = (33m/s)^2/6.0= 181 meters.

F.

## Homework Statement

In coming to a stop, a car leaves skid marks 92 m long on the highway. Assuming a decelration of 7.00m/s^2, estimate the speed of the car just before braking.

## Homework Equations

and## The Attempt at a Solution

V= √(2x7.00x92) ~ 36 m/s.

G.

## Homework Statement

Estimate how long it took King Kong to fall straight down from the tip of the Empire State building (380 m high) and his velocity just before landing.

## Homework Equations

and## The Attempt at a Solution

y=vot1 + 1/2 x gt

t= 8.8 seconds.

V^2=Vo^2 + 2gh

V = 86 meters/seconds.

H.

## Homework Statement

A ballplayer catches a ball 3.0 seconds after throwing it vertically upward. With what speed did he throw it, and what height did it reach?

## Homework Equations

and## The Attempt at a Solution

I don't know which equation to use here... Could you please tell me which one it is?

Thanks!