Question

A)

A student stretches an elastic band by 0.8 m in 0.5 seconds. The spring constant of the elastic band is 40 N/m. What was the power exerted by the student?

	25.6 W
	64.0 W
	12.8 W
	32 W

B)

A student pushes a 0.2 kg box against a spring causing the spring to compress 0.15 m. When the spring is released, it will launch the box vertically into the air. What is the maximum height the box will reach if the spring constant is 300 N/m?

	0.3 m
	5.8 m
	1.7 m
	3.4 m

C)

A student connects a 1 hp motor to a bicycle. How much time will it take for the bicycle to accelerate from rest to a speed of 5.0 m/s if the combined mass of the student and the bicycle is 120 kg? (1 hp = 746 W)

	0.5 s
	1500 s
	2.0 s
	300 s

Answer 1

A)

Given

The energy of the spring when it is compressed by an amount d is given by

the power exerted by the student is given by

B)

Given

we get from the conservation of energy

or,

Now let H be the maximum height that will be reached by the box.so

or,

or,

C)

Given

The energy is required to accelerate the bicycle from rest to a speed of 5m/s is given by

The time is required to accelerate the bicycle from the rest to a speed of 5m/s is