The initial kinetic energy of the cart is

(1)
where m is the mass of the cart and v its initial velocity.
Then, the cart hits the spring compressing it. The maximum compression occurs when the cart stops, and at that point the kinetic energy of the cart is zero, so all its initial kinetic energy has been converted into elastic potential energy of the spring:

where k is the spring constant and x is the spring compression.
For energy conservation, K=U. We can calculate U first: the compression of the spring is x=60 cm=0.60 m, while the spring constant is k=250 N/m, so

So, the initial kinetic energy of the cart is also 45 J, and from (1) we can find the value of the initial velocity:
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Answer:
sorry- but what........?!
Resistance=voltage/current
so 21.0/3.0=7
your answer would be in ohms
Hope this helped a little:)
Answer:
Explanation:Assume you are lifting an object with mass 20 kg from the ground to a height of 1.5 m. Assume that you are exerting a constant force in the upward direction and that you are moving the object upward with uniform velocity. The net force on the object is zero. The force you are exerting is equal in magnitude and opposite in direction to the force of gravity. As you are lifting the object you are doing work on the object.