# Holt Hw

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• Published : November 28, 2012

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Hw #M10: Holt p. 58 #3, 5; p. 64 # 1,5

A car accelerates uniformly in a strait line from rest at the rate of 2.3m/s^2. a. What is the speed of the car after 55m?
Vf^2= Vi^2+2ad Vf= 2(2.3m/s^2)(55m)= 253m, √253m= 16m/s

b. How long does it take the car to travel 55m?
t= (2∆d)/ (Vi+Vf) t= 2(55m)/ (0+16m/s)= 6.9sec

An aircraft has a liftoff speed of 20km/h. What minimum uniform acceleration does this require if the aircraft is to be airborne after a takeoff run of 240m?

a. a= (Vf^2- Vi^2)/ 2d= ((120km/h)^2- (0)^2)/ 2(0.24km)= 3.0x10^4 km/h^2= 2.3m/s^2

1. A robot probe drops a camera of the rim of a 239m high cliff on Mars, where the free- fall acceleration is -3.7m/s^2.

a. Find the velocity which the camera hits the ground.
Vf^2= Vi^2+2ad= 2(-3.7m/s^2)(239m)= √1768.9m/s = 42m/s

b. Find the time required for it to hit the ground
t= (2∆d)/ (Vi+Vf)= 2(230m)/ (0+42m/s)= 11sec

Maria throws an apple vertically upward from a height of 1.3m with an initial velocity of 2.4m/s. a. Will the apple reach a friend in a treehouse 5.3m about the ground? d= (Vf^2- Vi^2)/ 2a= (0- (2.4m/s)^2)/ (2)(9.81m/s^2)= .2936m .2936m+1.3m= 1.6m. No, it will not reach the friend in the treehouse.

b. If the apple is not caught, how long will the apple be in the air before it hits the ground?
tup= (Vi-Vf)/a t= 0-(2.4m/s)/ (9.81m/s^2)= .24sec.