1.Easy
A hoist lifts a 100 kg load at constant speed through a height of 4 m in 60 s. Find the average power P it delivers to the load, in W.
m = 100 kgh = 4 mt = 60 sg = 9.81 m/s²
P = W
Work & energy worksheet with answers
2.Easy
A 2.5 kg ball is dropped from rest from a height of 35 m. Ignore air resistance. Find its kinetic energy Ek just before it hits the ground.
m = 2.5 kgh = 35 mg = 9.81 m/s²
Ek = J
3.Medium
A 5 kg block slides 7 m down a slope at 45° to the horizontal, with a coefficient of kinetic friction of 0.4. Find the work Wf done against friction.
m = 5 kgθ = 45°μ = 0.4d = 7 mg = 9.81 m/s²
Wf = J
4.Medium
A car travelling at 30 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 0.5. Find the stopping distance d.
v = 30 km/hμ = 0.5g = 9.81 m/s²
d = m
5.Hard
A 0.5 kg block is released from rest at height 4.5 m on a smooth ramp. At the bottom it crosses a rough horizontal strip 4.5 m long (μ = 0.25) and then runs onto a spring (k = 500 N/m) on a smooth surface. Find the speed v of the block when it reaches the spring.
m = 0.5 kgh = 4.5 mL = 4.5 mμ = 0.25k = 500 N/mg = 9.81 m/s²
v = m/s
6.Hard
An 8 kg block rests on a rough horizontal table (μ = 0.2). A light string runs from it over a smooth pulley at the edge of the table to a hanging 6 kg block. The system is released from rest. Find the speed v of the blocks after the hanging block has dropped 3 m.
m1 = 8 kgm2 = 6 kgμ = 0.2d = 3 mg = 9.81 m/s²
v = m/s
Answer key
- 1. P = 65.4 W
- 2. Ek = 858.4 J
- 3. Wf = 97.11 J
- 4. d = 7.079 m
- 5. v = 8.137 m/s
- 6. v = 4.301 m/s
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