1.Easy
A hoist lifts a 400 kg load at constant speed through a height of 7 m in 20 s. Find the average power P it delivers to the load, in kW.
m = 400 kgh = 7 mt = 20 sg = 9.81 m/s²
P = kW
Work & energy worksheet with answers
2.Easy
A 5 kg block slides at 5 m/s on a smooth horizontal surface into a spring of stiffness 500 N/m. Find the maximum compression x of the spring, in cm.
m = 5 kgv = 5 m/sk = 500 N/m
x = cm
3.Medium
A block slides from rest down a slope at 45° to the horizontal. The coefficient of kinetic friction is 0.2. Find its speed v after it has slid 15 m along the slope.
θ = 45°μ = 0.2d = 15 mg = 9.81 m/s²
v = m/s
4.Medium
A car travelling at 120 km/h on a level road brakes hard and skids to a stop with its wheels locked. The coefficient of kinetic friction between the tyres and the road is 0.8. Find the stopping distance d.
v = 120 km/hμ = 0.8g = 9.81 m/s²
d = m
5.Hard
A 2 kg block is released from rest at height 2 m on a smooth ramp. At the bottom it crosses a rough horizontal strip 2 m long (μ = 0.1) and then runs onto a spring (k = 800 N/m) on a smooth surface. Find the maximum compression x of the spring.
m = 2 kgh = 2 mL = 2 mμ = 0.1k = 800 N/mg = 9.81 m/s²
x = cm
6.Hard
A 1 kg block is released from rest at height 4 m on a smooth ramp. At the bottom it crosses a rough horizontal strip 1 m long (μ = 0.1) and then runs onto a spring (k = 1000 N/m) on a smooth surface. Find the maximum compression x of the spring.
m = 1 kgh = 4 mL = 1 mμ = 0.1k = 1000 N/mg = 9.81 m/s²
x = cm
Answer key
- 1. P = 1.373 kW
- 2. x = 50 cm
- 3. v = 12.9 m/s
- 4. d = 70.79 m
- 5. x = 29.71 cm
- 6. x = 27.66 cm
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