Mechanics

Force – Impulse – Momentum

Hi All! I’m having mega problems with one part of a physics assignment. Looking for any help.
The details are as follows:

The diagram shows the normal force on Christine’s feet vs. time, as recorded by a force plate while she stands still initially (until point B), then jumps off the plate. (This trial is separate from the one in the previous problem. The graph is over-simplified and idealised, compared to reality.) When her feet leave the plate, the normal force is zero.

1)What is the magnitude of the (upward) impulse generated by the normal force of Christine during the time interval of her jump off the plate?

2)What is the magnitude of the downward impulse due to gravity during this interval?

3)What is the net impulse which propels her upwards when she jumps off the plate? (Recall, the net force on her is the normal force minus the force of gravity.)

4)What is her change in speed upwards for this process?

The graph has NORMAL FORCE (N) on the y-axis and TIME (s) on the X axis.
The line is at a constant 550 N until point B (1.75 seconds) at which time it shoot up vertically to 1550 N at a time of 1.95 seconds. It peaks at this time and position then drops down to 0 N at 2.15 seconds.

Thanks in advance for any guidance that can be provided!

… Sara

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Why are you hurt more when you punch a wall then when you punch a sponge?

Why are  you hurt more when you punch a wall then when you punch a sponge?

Asked Shivangi

Answer:

This is explained on the basis of impulse momentum principle.

Impulse of a force is the product of Force and time and is equal to the change in momentum produced.

The overall effect of a force is the change in momentum produced.

When we are punching, the effect on hitting is the stopping of the fist moving initially with a particular speed.

So, if we hit on a wall, the change in momentum takes place in a small interval of time and therefore the average force involved is very large and therefore it hurts.

When we hit on a sponge, the time taken will be more and the average force will be less and therefore it hurts less.

Momentum and Kinetic Energy

How it is possible to double the momentum of a body by increasing the kinetic energy four times?at the time what happen to mass?

Answer:

When we say, KE is increased, we mean to say by increasing speed alone unless otherwise specified.

Here mass remains constant.

Please note that the question says, KE of a body increased 4 times; which suggests that the body is the same and KE is increased by increasing the speed alone.

Physics of Diving

When a high diver in a swimming event springs from the board and “tucks in”, a rapid spin result. Why is this?

Answer: This is the consequence of conservation of angular momentum.

The angular momentum of a body is the product of Moment of inertia (A measure of rotational inertia and it depends on the mass as well as distribution of mass about the axis of rotation. Farther the masses, greater will be the rotational inertia) and the angular velocity (The speed of rotation)

The angular momentum of a body remains unchanged in the absence of any external torque.

When the diver dives, he is giving his body a turning and takes off with his limbs stretched. In the stretched position, the moment of inertia is more. When he “tucks in”, the moment of inertia decreases. But since this happens without any external torque, it would result in an increase in angular velocity so as to keep the angular momentum constant.