1. How much work is done to lift 10 boxes that weigh 100N each to a height of 2.
ID: 1646343 • Letter: 1
Question
1. How much work is done to lift 10 boxes that weigh 100N each to a height of 2.0m?
2. How much energy must a 1500kg car’s engine provide to accelerate it from 20m/s to 25m/s?
3. Refer to #2. When measured, it takes 25000J more energy than calculated. Why?
4. A water balloon slingshot is used to shoot a 200g water balloon 25m straight up. If the slingshot is stretched 50cm, what is the spring constant of the slingshot and how much energy is stored in the elastic bands? k = ______________ Uelas = ______________
5. Assuming no friction, how much work must be done to push a 6.0m diameter merry-go-round with a moment of inertia of 500kgm2, from rest to a rotational speed of .50rad/s?
Explanation / Answer
1.
w = mg = weight of each box = 100 N
h = height to which box are lifted = 2 m
n = number of boxes = 10
work done is given as
W = n wh
W = 10 x 100 x 2
W = 2000 J
2.
m = mass of the car = 1500 kg
vi = initial speed = 20 m/s
vf = final speed = 25 m/s
Energy needed to accelerate is given as
E = (0.5) m (vf2 - vi2)
E = (0.5) (1500) ((25)2 - (20)2)
E = 168750 J
3.
This is because while solving question 2 , we ignored the presence of friction and air resistance. But in actual, we have friction and air resistance both present. hence some work must be done to come over these forces too. That extra work of 25000 J is nothing but this work done against these forces.
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