Download Forces and Energy Homework File

1. The diagram shows a boy pushing a box in a warehouse.
A force of 10 N is required to
overcome friction between the box
and the floor.
Any extra force applied to the box
makes the box accelerate.
(a) If the boy pushes with a force of 30 N:
(i)
Draw on the diagram the two horizontal forces acting on the block [2]
(ii)
Calculate the resultant force acting on the box.
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(iii)
Write down a formula which links mass, acceleration and resultant
force.
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(iv)
Calculate the acceleration of the box.
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(b) As the box increases in speed the friction force also increases. Eventually
the friction force balances the push force exerted by the boy.
(i)
What is the size of the friction force now?
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(ii)
What is the size of the resultant force?
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(iii)
Describe the motion of the box.
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(c) Suggest a way of reducing the friction between the box and the floor.
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(d) Not all the energy is transferred to the box. Into what other forms is this
energy converted?
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2. (a) Name two vertical forces acting on a raindrop falling through the air.
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(b) Explain why the raindrop eventually moves with constant velocity
towards the ground.
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3. A rocket of mass 100 kg has two forces acting on it as it moves vertically
upward just after lift off; its own weight force and the thrust of the rocket
engines, which is 3000N.
(a) Draw a diagram showing the two forces acting on the rocket.
(b) Use the value of the mass to calculate the weight of the rocket.
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(c) At take off calculate the resultant force acting on the rocket.
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(b) Use the equation for Newton’s second law to calculate the initial
acceleration of the rocket at take off.
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4. An electric motor is used to lift a bag of
cement of weight 200N through a vertical
distance of 5 metres.
(a) Write down, in words, the equation linking
force, distance and work done.
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(b) Calculate the work done in lifting the cement.
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(c) The motor supplied 10,000 J of energy in the lifting of the cement.
5.
(i)
How much energy was wasted or not usefully transferred?
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(ii)
State and explain what has happened to the wasted energy during
the transfer.
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6. A type of toy catapult consists of a movable
plunger attached to a spring. The handle was
pulled down to fully compress the spring and
then released.
The ball of mass 0.1 kg was projected 0.75 m
vertically into the air. (Take g=10N/kg)
(a) Describe the energy changes that take place
when the handle is released.
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(b) Calculate the maximum gravitational potential energy gained by the ball.
(Write down any formula that you use and show your calculations)
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(c) Use the concept of energy transfer to calculate the speed of the ball as it
left the plunger.
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