A boy sledges down a hill. The boy and his sledge have a combined mass of $85 \mathrm{kg}$. He starts from rest and descends through a vertical height of $3 \mathrm{m}$. Friction and air resistance are negligible. Find the work done by gravity. (Use $g=10 \mathrm{m} {\mathrm{s}}^{-2}$)

A boy sledges down a hill. The boy and his sledge have a combined mass of $85 \mathrm{kg}$. He starts from rest and descends through a vertical height of $3 \mathrm{m}$. Friction and air resistance are negligible.

Use the work-energy principle to find the boy's speed at the end of the descent. (Use $g=10 \mathrm{m} {\mathrm{s}}^{-2}$)

A boy sledges down a hill. The boy and his sledge have a combined mass of $85 \mathrm{kg}$. He starts from rest and descends through a vertical height of $3 \mathrm{m}$. Friction and air resistance are negligible.

Find their speed at the end of the descent.

A girl of mass $50 \mathrm{kg}$ travels down a water slide. She starts at the top with a speed of $2 \mathrm{m}{ \mathrm{s}}^{-1}$ and descends through a vertical height of $5 \mathrm{m}$.

Assuming that there is no resistance, find her speed when she reaches the bottom of the slide.

A girl of mass $50 \mathrm{kg}$ travels down a water slide. She starts at the top with a speed of $2 \mathrm{m}{ \mathrm{s}}^{-1}$ and descends through a vertical height of $5 \mathrm{m}$.

The girl's actual final speed is $8 \mathrm{m}{ \mathrm{s}}^{-1}$ because there is resistance of average value $40 \mathrm{N}$. Find the length of the water slide.

A child of mass $45 \mathrm{kg}$ travels down a water chute. The child has speed $1 \mathrm{m}{ \mathrm{s}}^{-1}$ at the top of the chute and speed $5{ \mathrm{ms}}^{-1}$ at the bottom of the chute. The length of the water chute is $20 \mathrm{m}$ and the height through which it descends is $4 \mathrm{m}$. Work out the average resistance force that acts.

A boy sits on a sledge at the top of an icy hill. He gently sets the sledge in motion. When he reaches the bottom of the hill he is moving at $10 \mathrm{m}{ \mathrm{s}}^{-1}$. Assuming that friction is negligible, find the height of the hill.

A girl of mass $50 \mathrm{kg}$ sits on a sledge at the top of a grassy hill. She gently sets the sledge in motion. When she reaches the bottom of the hill she is moving at $9.9 \mathrm{m}{ \mathrm{s}}^{-1}$. The hill is $5 \mathrm{m}$ high and the sledge slides $100 \mathrm{m}$ down the hill. Work out the resistance force. (Use $g=10 \mathrm{m} {\mathrm{s}}^{-2}$)

A girl of mass $50 \mathrm{kg}$ sits on a sledge at the top of a grassy hill. She gently sets the sledge in motion. When she reaches the bottom of the hill she is moving at $9.9 \mathrm{m}{ \mathrm{s}}^{-1}$. The hill is $5 \mathrm{m}$ high and the sledge slides $100 \mathrm{m}$ down the hill.

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