Practice 4B: | 1 | 2 |
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**Newton's Second Law, By Krista Heim, 2001**

**1. The net external force on the propeller of
a 3.2 Kg model airplane is 7.0N forward. What is the acceleration of the
airplane? **

Here's what you know, m=3.2 kg, F=7.0 N, use the formula F = ma, so 7.0=3.2a, solve for a, a=2.2 m/s^2 forward.

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**2. The net external force on a golf cart is 390 N
north. If the cart has a total mass of 270 Kg, what are the magnitude and
direction of its acceleration?**

Here's what you know, F= 390 N north, m=270 kg, use the formula F = ma, 390=270a, solve for a, a=1.4 m/s^2 to the north.

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**3. A car has a mass of 1.5X10^3 Kg. If
the force acting on the car is 6.75X10^3 N to the east, what is the car's
acceleration? **

Here's what you know, m=1.5X10^3 kg, F= 6.75X10^3 N east, use the formula F = ma, 6.75X10^3=1.5X10^3a, solve for a, a=4.5 m/s^2 to the east.

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**4. A 2.0Kg otter starts from rest at the top
of a muddy incline 85cm long and slides down to the bottom in 0.50 s. What
net external force acts on the otter along the incline?**

Here's what you know, m=2.0 kg, v

_{i}=0m/s,Dx=.85 m, Dt=5 s, to find a, use the formula Dx = v_{i}(Dt) +^{1}/_{2}a(Dt)^{2},0.85=0(.5)+1/2a(.50)^2, solve for a, a=6.8 m/s^2. Now use the formula F = ma, F=2.0*6.8, solve for F, F=14 N.

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**5. A soccer ball kicked with a force of 13.5 N
accelerates at 6.5 m/s^2 to the right. What is the mass of the
ball? **

Here's what you know, F=13.5 N, a=6.5 m/s^2 to the right, use the formula F = ma, 13.5=6.5m, solve for m, m=2.1 kg.

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