Question 1

Why is the work done by the spring positive during the launch?

Accepted Answer

During launch, the spring force on the block and the block's displacement point in the same direction, so W_s = -delta U_s = +1/2 kx^2. The block does negative work on the spring, while the spring does positive work on the block.

Question 2

What is the speed of a block released from a compressed spring?

Accepted Answer

For a frictionless rail, energy conservation gives 1/2 kx^2 = 1/2 mv^2. Thus, if the block starts from rest, its speed at the spring's natural length is v = x sqrt(k/m).

Question 3

How does increasing the compression affect spring energy?

Accepted Answer

Spring energy is U_s = 1/2 kx^2, so it varies with the square of compression. For unchanged k, doubling x stores four times as much energy and produces twice the launch speed from rest.

Question 4

Why does instantaneous power not remain high throughout the launch?

Accepted Answer

The power delivered by the spring to the block is P_to = F_s . v, where F_s is the spring force on the block. It is zero at release because v = 0, becomes positive and reaches a maximum between the endpoints, and returns to zero at natural length because F_s = 0.

Question 5

What happens to an ideal compression spring at natural length?

Accepted Answer

At natural length its extension from equilibrium is zero, so U_s = 0 and F_s = 0. It has reached its natural position and separates from the block rather than pulling it farther.

Spring Launch: Work, Energy & Power

About this lab

Practice