Physics Question?

Question

A 2.8 kg block slides with a speed of 1.1 m/s on a frictionless, horizontal surface until it encounters a spring.

(A) If the block compresses the spring 5.7 cm before coming to rest, what is the force constant of the spring?

(B) Find the greatest height of the rock as measured from the base of the cliff.

Ok, I feel rather dumb for not being able to get this, but I get the wrong answer every time. Help please!

Answer 1

The block has a kinetic energy of (1/2)2.8*1.1² = 1.694J. The spring, at the point the block stops, contains all of this energy as potential energy and (1/2)kx² is the expression for this. So
(1/2)k*.57² = 1.694 => k = 10.337 N/m.

Don't know about (B) since there aren't any details.

Doug

Answer 2

Not sure if I understand this situation. If the block is sliding on a frictionless, it would be accelerating. And you say that its speed is 1.1 m/s. I guess that you mean that it's the speed at the moment it gets to the spring.

If this is what you ment, then the kinetic energy at that moment must be equals to the potential energy when the block began to slide if its initial speed was 0.

E = mgh = mv^2/2

gh = v^2 / 2

h = g v^2 / 2

Ilusion