• Oct 8th 2008, 01:05 AM
scienceteacher

http://i38.tinypic.com/5bw8hv.jpg
• Oct 8th 2008, 07:28 AM
hjelliott
Quote:

1. How far will a ball travel if a baseball thrower pitches a ball at 43 ms^-1 in 4.2s?
One general kinematics equation for an object at uniform speed is v(speed[in m/s])=d(distance[in m])/t(time[in s]). If v=d/t, then that can be rearranged to d=vt. We're given a speed (43 ms^-1) and a time (4.2s). If we multiply the speed and the time, (43ms^-1 x 4.2s) we get 180.6 m, or with significant figures, you would have 1.8 x 10^2

Quote:

2. How long would it take to produce 150 kW with 780 J of energy?
It is given there that Power (watts) = Energy (joules)/time (seconds)
The metric Kilo prefix means 1000 times so 150 kW means 150 x 1000 watts which is 150,000 W.
If P=E/t, then that rearranged to find time would be t=E/P. The Energy we know is 780 J and the Power we found is 150,000 W. 780 J/150,000W = 0.0052 Seconds.

Quote:

3. What is the net force needed to accelerate a 5800 g, 6.2 ms^-2?
One known dynamics thing is that acceleration is both known as ms^-2 as well as NKg^-1.
It's given that Force (Newtons) = Mass (Kg) x Acceleration (ms^-2 OR NKg^-1). We're given the mass of the objet in grams so we need to convert that to kilograms so we divide the number by 1000 giving us 5.8 kg.
The formula given F=ma is what we need so F = 5.8kg x 6.2 NKg^-1 = 35.96 N. With significant figures, that would round to 36 N.

I hope my first bit of advice on this forum was of help to you.

- Jordan
• Oct 9th 2008, 03:22 AM
scienceteacher
Hi
(Happy)Thanxx Hjelliot your a awesome guy(Happy)