# Various physics questions

1. ### mikefitz

156
My professor insists on lecturing about tension and pulleys all week, then he assigns us problems that have no relation to lecture

I'm having trouble with a few problems, hopefully you can help me.

Grant Hill jumps 1.2 m straight up into the air to slam-dunk a basketball into the net. With what speed did he leave the floor?

This one I'm not sure where to begin. d=1.2 - don't I need time in order to calculate speed?

During a walk on the Moon, an astronaut accidentally drops his camera over a 18.5 m cliff. It leaves his hands with zero speed, and after 2 s it has attained a velocity of 3.6 m/s downward. How far has the camera fallen after 4.1 s?

Interesting. I know that the gravitational constant on the moon is 1.62m/s^2, but I don't know how that comes in to play in regards to calculating the distance. Any ideas?

A 2.0-kg ball tied to a string fixed to the ceiling is pulled to one side by a force (the figure below ). Just before the ball is released and allowed to swing back and forth, (a) how large is the force that is holding the ball in position and (b) what is the tension in the string?

I tried T=2(sin30)+2(cos30)= 2.732kg this is apparently wrong.

What do I need to do here?

A marble is rolled so that it is projected horizontally off the top landing of a staircase. The initial speed of the marble is 3.0 m/s. Each step is 0.18 m high and 0.30 m wide. Which step does the marble strike first?

Do I just calculate the horizontal component and divide by the width of the steps?

If you have ANY idea about any of these please let me know. thanks

2. ### mikefitz

156
*just a bump before i go to bed*

these problems are due tomorrow at 7:30 AM, I am going to check back here at 6 and see if there are any responses. I don't think anyone will want to help on all four, so if you have any idea on any specific problem I would really appreciate the help.

3. ### andrevdh

1,670
I would attempt the first one with energy conservation. That is he gives himself a certain amount of kinetic energy before leaving the ground. All of this kinetic energy will then be converted to potential energy at the top of his motion.

For the camera one use constant acceleration equations. The first bit of information enable you to calculate the gravitational acceleration on the moon, assuming it dropped out of rest by using

$$v=u+at$$

then use

$$s=ut+0.5at^2$$

to calculate the distance falled.

With the ball problem you are in serious trouble - too much to learn! What will the horizontal and vertical components of the tension in the string be if the magnitude of the tension is T?

With the marble you need to apply projectile motion theory.

4. ### Delzac

389
Anyway for the ball problem, all the forces on the ball must in equal, in the sense of horizontal forces must cancel out to give zero, for the ball to be in equilibrium.

you that there is a force F in the positive X axis direction. To balance out, the tension must provide an equal and opposite F in the negative X axis direction.

Same applies to your weight, which is the vertical force pointing downwards. your tension too provides an equal and opposite force to cancel out ur weight.