Bridges & Cantilevers
What name do we give a force that stretches or pulls something?
Tension
A parachute increases which force?
Air resistance
What is the upward force a liquid puts on a floating object?
Upthrust (the buoyant force)
What is the energy of a moving object called?
Kinetic energy
Give the formula for speed
speed = distance ÷ time
In a loaded cantilever, which edge only expereinces tension, the top or the bottom?
The top (the bottom also experiences compression)
Explain why a soft landing means a smaller force on the egg.
Longer stopping time for the same change in momentum, so a smaller force (F = change in p ÷ time).
Name the two forces on a floating boat and say how they compare.
Weight and upthrust, equal and balanced.
What energy change happens as an egg falls?
Gravitational potential energy changes to kinetic energy.
What does a horizontal line on a speed-time graph tell you?
The object is moving at constant speed (no acceleration).
Why are triangles used in bridges and cranes?
They are rigid: a triangle can’t change shape unless a side bends or breaks.
Give the formula for momentum.
Why does a steel ship float but a steel paperclip sink
The ship is hollow, so it displaces a lot of water and its average density is below water. The paperclip is denser than water and displaces very little.
Where does the egg’s energy go when it lands in padding? Use conservation of energy.
It isn’t lost. It becomes deformation of the padding, heat and sound.
Use Newton’s 1st law (or otherwise) to explain why you lurch forward when a bus brakes suddenly.
Your body keeps moving at the same speed until a force acts on it. The bus slows but you don’t.
Most bridges held 1 N but became unbalanced as more weight went on. Give two possible reasons.
Accept any of: the load was off-centre, one side or joint carried more, joints slipped, thin parts buckled.
An egg padded top and bottom still broke because it landed on its side. Explain why and suggest a redesign
The unprotected side took the impact, so the forces weren’t balanced. Pad evenly all round, or add fins or a parachute to keep it upright.
Your boat sank as more weights were added. Explain what happened in terms of weight, upthrust and displaced water, and how to carry more.
Weight grew until it exceeded the biggest upthrust the boat could get. More volume below the rim, higher sides, a wide base and an even load all help.
A ball has 3 J of gravitational potential energy at the top of a drop. Ignoring air resistance, how much kinetic energy does it have just before landing?
3 J, by conservation of energy
A cyclist moves at constant speed along a flat road. Is there a resultant force? Compare the forces acting.
No resultant force. The driving force equals the resistive forces (air resistance and friction), and the weight equals the normal reaction.
Your cantilever keeps tipping off the table. Suggest two changes and explain why they help.
Any two: a heavier or bigger anchored end, a longer anchored section, shorter overhang, triangulation.
Calculate the momentum of a 0.06 kg egg falling at 10 m/s
p = 0.06 × 10 = 0.6 kg m/s
A block has a mass of 200 g and a volume of 50 cm³. Find its density. Will it float in water?
200 ÷ 50 = 4 g/cm³, which is more than 1 g/cm³, so it sinks.
Calculate the gravitational potential energy of a 0.06 kg egg 5 m up (g = 9.8).
0.06 × 9.8 × 5 ≈ 2.9 J
A 2 kg trolley accelerates at 3 m/s². What is the resultant force?
F = ma = 2 × 3 = 6 N