1.Easy
A hoist lifts a 200 kg load at constant speed through a height of 16 m in 15 s. Find the average power P it delivers to the load, in kW.
m = 200 kgh = 16 mt = 15 sg = 9.81 m/s²
P = kW
Work & energy worksheet with answers
2.Easy
A 5 kg ball is dropped from rest from a height of 12 m. Ignore air resistance. Find its speed v just before it hits the ground.
m = 5 kgh = 12 mg = 9.81 m/s²
v = m/s
3.Medium
A toy launcher has a vertical spring of stiffness 1500 N/m. A 0.2 kg ball is placed on it and the spring is compressed by 3 cm, then released. Ignoring air resistance and the spring’s mass, find the height h the ball rises, measured from its position when the spring was compressed.
m = 0.2 kgk = 1500 N/mx = 3 cmg = 9.81 m/s²
h = m
4.Medium
A block slides from rest down a slope at 35° to the horizontal. The coefficient of kinetic friction is 0.2. Find its speed v after it has slid 2 m along the slope.
θ = 35°μ = 0.2d = 2 mg = 9.81 m/s²
v = m/s
5.Hard
A spring of stiffness 500 N/m at the bottom of a 25° slope is compressed by 20 cm against a 2 kg block and released. The coefficient of kinetic friction between block and slope is 0.3. How far d up the slope does the block travel from the release point before it stops? (Ignore the short distance over which the spring pushes, i.e. take friction and gravity over the whole distance d.)
m = 2 kgk = 500 N/mx = 20 cmθ = 25°μ = 0.3g = 9.81 m/s²
d = m
6.Hard
A 2 kg block starts from rest at the bottom of a 30° slope and is pulled up the slope by a constant force of 25 N parallel to the slope. The coefficient of kinetic friction is 0.2. Find the speed v of the block after it has moved 2 m up the slope.
m = 2 kgF = 25 Nθ = 30°μ = 0.2d = 2 mg = 9.81 m/s²
v = m/s
Answer key
- 1. P = 2.093 kW
- 2. v = 15.34 m/s
- 3. h = 0.344 m
- 4. v = 4.01 m/s
- 5. d = 0.7339 m
- 6. v = 4.856 m/s
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